The construction and utilization of the fourth-generation ultrafast electron diffraction apparatus, UED4, is the subject of this thesis. With UED4 and its novel and universal sample delivery method based on laser desorption, we were able to vaporize thermally labile molecular samples and determine their ground-state structures and the structures of their photochemical and photophysical reaction products. Each component part of the new UED4 apparatus is described, and the experimental and computational procedures used to extract structural information from the time-resolved diffraction patterns are presented.
\r\n\r\nSeveral molecules were studied in their ground states and photoinduced excited states or product states on the time scale of picoseconds and nanoseconds. With UED3, nitrobenzene was shown to undergo intramolecular rearrangement prior to NO loss in an ultrafast fragmentation reaction. In indole, the chromophore of the amino acid tryptophan, the involvement of a dark structure, formed on the picosecond time scale, was revealed in the nonradiative decay pathway of the initially excited state. By determining the ground state structures of the thermally labile nucleobases uracil and guanine, the first use of surface-assisted laser desorption in a pulsed electron diffraction experiment was reported using the newly developed UED4 apparatus. The determined structures of the photochemically generated species of the photochromic molecule 6-nitro-BIPS further demonstrated the capability of laser desorption electron diffraction to function as a time-resolved experiment. Finally, the fragmentation reaction of the amino acid tryptophan upon UV laser irradiation was studied with UED4. The ability to deliver increasingly large and conformationally heterogeneous molecules into the gas phase now provides new challenges and opportunities of both experimental and theoretical nature for the field of ultrafast electron diffraction.
", "doi": "10.7907/YACJ-HG30", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:6156", "collection": "thesis", "collection_id": "6156", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10242010-143824484", "primary_object_url": { "basename": "Full_thesis.pdf", "content": "final", "filesize": 98888164, "license": "other", "mime_type": "application/pdf", "url": "/6156/9/Full_thesis.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Biochemical and Biophysical Characterizations of Immunoglobulin Superfamily Receptors Neogenin and L1", "author": [ { "family_name": "Yang", "given_name": "Fan", "clpid": "Yang-Fan" } ], "thesis_advisor": [ { "family_name": "Bjorkman", "given_name": "Pamela J.", "orcid": "0000-0002-2277-3990", "clpid": "Bjorkman-P-J" } ], "thesis_committee": [ { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Phillips", "given_name": "Robert B.", "orcid": "0000-0003-3082-2809", "clpid": "Phillips-R" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Bjorkman", "given_name": "Pamela J.", "orcid": "0000-0002-2277-3990", "clpid": "Bjorkman-P-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Immunoglobulin (Ig) superfamily receptors function in a wide variety of developmental and metabolic processes. We are particularly interested to characterize two Ig superfamily receptors neogenin and L1. The first chapter of the thesis gives a brief review of the biological significance of neogenin and L1 and what has been learned in their functions. In Chapter 2, we described the localization of the hemojuvelin-binding epitope of neogenin to the membrane proximal fifth and sixth fibronectin type III (FNIII) domains, with the sixth FNIII domain contributing the majority of the binding. Chapter 3 presents the crystal structure of this hemojuvelin-binding fragment at 1.8 \u00c5, revealing a nearly linear domain arrangement. Hemojuvelin binding sites have been mapped to one face of the sixth FNIII domain based on sequence alignment between neogenin and DCC (Deleted in Colorectal Cancer), a molecule related to neogenin but does not bind to hemojuvelin. These results should also be informative in understanding the interaction between neogenin and repulsive guidance molecule (RGM), the closest homologue of hemojuvelin. The interaction between neogenin and RGM is known to regulate neuronal survival. Chapter 4, the second part of the thesis, describes our studies of L1-mediated homophilic adhesion using biophysical approaches. We built a basis shape model to describe L1-mediated homophilic adhesion between L1-coated giant unilamellar vesicles and flat substrate. Using confocal microscopy techniques, we were able to reconstruct the three-dimensional shape of an adhered vesicle. We developed an algorithm in order to derive adhesion strength from the configurations of adhered vesicles based on our basis shape model using energy minimization approach.", "doi": "10.7907/Q8ET-K632", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:6432", "collection": "thesis", "collection_id": "6432", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-091250250", "primary_object_url": { "basename": "Thesis_Peigen.pdf", "content": "final", "filesize": 11678980, "license": "other", "mime_type": "application/pdf", "url": "/6432/8/Thesis_Peigen.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Surface Chemistry at the Nanometer Scale", "author": [ { "family_name": "Cao", "given_name": "Peigen", "clpid": "Cao-Peigen" } ], "thesis_advisor": [ { "family_name": "Heath", "given_name": "James R.", "clpid": "Heath-J-R" } ], "thesis_committee": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" }, { "family_name": "Heath", "given_name": "James R.", "clpid": "Heath-J-R" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_chem" } ], "abstract": "This thesis describes research towards understanding surface chemical and physical processes, as well as their effects on the underlying substrate properties, at the nanometer and atomic scales. We demonstrate a method to tune the density of etch pits on Si(111) during the chlorination process so as to change the surface reactivity. Subsequent grafting of an azide group to replace chlorine demonstrates an example of non-oxidative passivation of silicon surfaces with new functionalities. Depending upon the solvent used in the azidation process, it is shown to yield different azidation kinetic rates, different final azide coverages, and different surface-area distributions. Scanning tunneling spectroscopy studies show that both chlorination and azidation processes significantly modify the surface electronic structures, with the former leading to a non-zero density of states at the Fermi level.\r\n
\r\nOur studies on a new class of corrugation, i.e., wrinkles, in exfoliated graphene on SiO2 show that a \"three-for-six\" triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle is a perturbation that breaks the six-fold symmetry of the graphene lattice. Lower electrical conductance is also found on the top of wrinkles compared to other regions of graphene. The wrinkles are characterized by the presence of midgap states, which is in agreement with recent theoretical predictions. A general method is also reported for reliably fabricating ultrahigh-density graphene nanoribbon (GNR) arrays. We have clearly observed how the properties of GNRs evolve as a function of number of graphene layers. The band gap (and so the on-off ratio) decreases as the number of layers increases. These results suggest that, in addition to single layer graphene, properties of GNRs of different thicknesses can also be harnessed for engineering GNRs as different building blocks towards FET applications.\r\n
\r\nA novel imaging technique, graphene-templated scanning probe microscopy, has been developed and applied for the study on the condensation process of water and small organic molecules on mica. We found that these molecular adlayers grow epitaxially on the mica substrate in a layer-by-layer fashion. In particular, submonolayers of water form atomically flat, faceted islands of height 0.37 plus or minus 0.02 nm, in agreement with the height of a monolayer of ice. The second adlayers also appear ice-like, and thicker layers appear liquid-like. This general mechanism, however, is not universal. Exclusively three-dimensional droplets of water are observed on chemically modified (hydrophobic) mica surfaces, suggesting a 3D growth mechanism.\r\n
\r\nThis thesis also includes my work on the design of a quartz-tuning-fork-based force sensor and related electronics for applications on low-temperature atomic force microscopy. Results show that the force-sensor-global-feedback circuit detector system induced lowest noise floor. The high detection sensitivity of this system demonstrates its ability to be used in frequency-modulated AFM at cryogenic temperatures. Surface topographic imaging of H-terminated Si(111) has been achieved at low temperatures.\r\n
", "doi": "10.7907/7EFV-V231", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:5824", "collection": "thesis", "collection_id": "5824", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05212010-154212167", "primary_object_url": { "basename": "thesis_VAN.pdf", "content": "final", "filesize": 1671048, "license": "other", "mime_type": "application/pdf", "url": "/5824/1/thesis_VAN.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Efficient Generation of Hyperpolarized Molecules Utilizing the Scalar Order of Parahydrogen", "author": [ { "family_name": "Norton", "given_name": "Valerie Ann", "clpid": "Norton-Valerie-Ann" } ], "thesis_advisor": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Rees", "given_name": "Douglas C.", "clpid": "Rees-D-C" }, { "family_name": "Reisman", "given_name": "Sarah E.", "clpid": "Reisman-S-E" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation describes methods that polarize the spin of a specific nucleus in molecules synthesized by molecular addition of parahydrogen to a precursor molecule. Nuclear magnetic resonance (NMR) pulse sequences are designed to perform efficient transfer of spin order by way of the scalar spin couplings between the two nascent protons and a heteronuclear spin label target. The result is an increase in the NMR signal from that nucleus by several orders of magnitude, approaching unity polarization. Algorithms are presented to effect the desired unitary evolution of this three-spin system over the range of couplings found in diverse molecules and in the presence of interfering spins. These methods are explored theoretically and comparisons are made to select the most advantageous method given a specific problem.
\r\n\r\nIssues concerning the choice of target molecule, portable equipment, and automation are discussed. Some design choices made for convenience in one aspect of the execution of the methods raise difficulties in other aspects. These difficulties are elucidated and methods of mitigation are discussed.
\r\n\r\nPulse design issues are elucidated with numerical calculations which confirm analytical results for the time dependence obtained in the multiply rotating frame approximation. Failures of this approximation at low frequencies are explored numerically leading to novel pulse sequence design rules which ameliorate undesirable phenomena peculiar to low field NMR, enabling its employment for this and other applications requiring precise control of the spin degrees of freedom. Experimental results, primarily aimed at biomedical applications, are reviewed.
\r\n", "doi": "10.7907/57FW-1060", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5276", "collection": "thesis", "collection_id": "5276", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08122009-151332", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 1729685, "license": "other", "mime_type": "application/pdf", "url": "/5276/1/thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Quantum Monte Carlo: Faster, More Reliable, and More Accurate", "author": [ { "family_name": "Anderson", "given_name": "Amos Gerald", "clpid": "Anderson-Amos-Gerald" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Miller", "given_name": "Thomas F.", "clpid": "Miller-T-F" }, { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The Schroedinger Equation has been available for about 83 years, but today, we still strain to apply it accurately to molecules of interest. The difficulty is not theoretical in nature, but practical, since we're held back by lack of sufficient computing power. Consequently, effort is applied to find acceptable approximations to facilitate real time solutions. In the meantime, computer technology has begun rapidly advancing and changing the way we think about efficient algorithms. For those who can reorganize their formulas to take advantage of these changes and thereby lift some approximations, incredible new opportunities await.
\r\n\r\nOver the last decade, we've seen the emergence of a new kind of computer processor, the graphics card. Designed to accelerate computer games by optimizing quantity instead of quality in processor, they have become of sufficient quality to be useful to some scientists. In this thesis, we explore the first known use of a graphics card to computational chemistry by rewriting our Quantum Monte Carlo software into the requisite \"data parallel\" formalism. We find that notwithstanding precision considerations, we are able to speed up our software by about a factor of 6.
\r\n\r\nThe success of a Quantum Monte Carlo calculation depends on more than just processing power. It also requires the scientist to carefully design the trial wavefunction used to guide simulated electrons. We have studied the use of Generalized Valence Bond wavefunctions to simply, and yet effectively, captured the essential static correlation in atoms and molecules. Furthermore, we have developed significantly improved two particle correlation functions, designed with both flexibility and simplicity considerations, representing an effective and reliable way to add the necessary dynamic correlation. Lastly, we present our method for stabilizing the statistical nature of the calculation, by manipulating configuration weights, thus facilitating efficient and robust calculations.
\r\n\r\nOur combination of Generalized Valence Bond wavefunctions, improved correlation functions, and stabilized weighting techniques for calculations run on graphics cards, represents a new way for using Quantum Monte Carlo to study arbitrarily sized molecules.
", "doi": "10.7907/KVTV-N754", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5447", "collection": "thesis", "collection_id": "5447", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12152009-120706357", "type": "thesis", "title": "Development and Applications of Quantum Monte Carlo", "author": [ { "family_name": "Fisher", "given_name": "Daniel Ross", "clpid": "Fisher-Daniel-Ross" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Okumura", "given_name": "Mitchio", "clpid": "Okumura-M" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Quantum Monte Carlo is a relatively new class of electronic structure methods that has the potential to calculate expectation values for atomic, molecular, and materials systems to within chemical accuracy. QMC scales as (ON3 or better with the size of the system, which is much more favorable than traditional electronic structure methods capable of comparable accuracy. In addition, the stochastic nature of QMC makes it relatively easy to parallelize over multiple processors.
\r\n \r\nQMC calculations use the Metropolis algorithm to sample the electron density of the system. This method has an inherent equilibration phase, during which the configurations do not represent the desired density and must be discarded. Because the time spent on equilibration increases linearly with the number of processors, this phase limits the efficiency of parallel calculations, making it impossible to use large numbers of processors to speed convergence.
\r\n \r\nThis thesis presents an algorithm that generates statistically independent walker configurations in regions of high probability density, shortening the length of the equilibration phase and ensuring the accuracy of calculations. Shortening the length of the equilibration phase greatly improves the efficiency of large parallel calculations, which will allow QMC calculations to use the next generation of homogeneous, heterogeneous, and distributed computing resources to conduct highly accurate simulations on large systems.
\r\n\r\nThe most common formulation of diffusion Monte Carlo has two sources of error: the time step used to propagate the walkers and the nodes of the trial function. In order to explore these sources of error, DMC calculations were carried out on three pericyclic hydrocarbon reactions using Hartree-Fock, generalized valence bond, and multiconfiguration self-consistent field trial functions and time steps ranging from 10-4 to 10-2 au. The results are compared to values from experiment and high quality ab initio calculations, as well as the recently developed X3LYP, M06, and XYG3 density functionals. The appropriate time step and trial functions for the reactants, transition states, and products are identified to begin to develop guidelines for researchers carrying out calculations on larger systems.
\r\n", "doi": "10.7907/4YCS-9T88", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:285", "collection": "thesis", "collection_id": "285", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01222009-173227", "primary_object_url": { "basename": "all-thesis.pdf", "content": "final", "filesize": 2602033, "license": "other", "mime_type": "application/pdf", "url": "/285/11/all-thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Isotope Effects in Chemical Processes of Atmospheric Interest", "author": [ { "family_name": "Chen", "given_name": "Wei-Chen", "clpid": "Chen-Wei-Chen" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The thesis is focused on the theoretical study of the isotope effects in three atmospheric reactions, the CO+OH reaction, the photolysis of N\u2082O, and the ozone formation. The CO+OH reaction is investigated by using both Rice-Ramsperger-Kassel-Marcus theory and its nonstatistical modification, which was prompted by existing molecular-beam data on incomplete intramolecular energy transfer in the HOCO* intermediate. The resulting calculations show reasonable agreement with most experimental data, except the O isotope effect. Two predictions are made: the temperature dependence of the OD+CO reaction; and the rate constant kv decreasing with increasing CO vibrational quantum number v from v = 0 to v = 1. In both experiments and our calculation, the kinetic oxygen isotope effect is different from the expected value (i.e. the mass-dependent slope), which may be due to the H-tunneling. An experiment that avoids a possible role of vibrationally excited OH radicals as reactants in the O isotope effect is also suggested to remove the discrepancy in the O isotope effect between the experiments and calculations.
\r\n\r\nThe UV photolysis of the greenhouse gas N\u2082O and its isotope effects are important in atmospheric chemistry. Based on the multidimensional reflection principle using the available ab initio data on the molecule for the potential energy surfaces and the transition dipole moments, we provide an accurate but not computationally intensive method in obtaining the absorption cross section. The present calculated fractionation gives good agreement with the experimental absorption cross section in the low-energy region, where the experimentally observed isotopic fractionation occurs. We also suggest a single effective mass, a linear combination of two main coordinates for the photolysis, to determine the slope of a multi-element isotope plot and to yield approximate agreement between the experimental data and a \"mass-dependent\" fractionation, which range from 0.47 to 3.28.
\r\n\r\nA modified ab initio potential energy surface is used for calculations of ozone recombination and isotopic exchange rate constants. The calculated low-pressure isotopic effects on the ozone formation reaction are consistent with the experimental results and with the theoretical results obtained earlier [J. Chem. Phys. 116, 137 (2002)]. This result showed that they are relatively insensitive to the properties of the PES.
\r\n", "doi": "10.7907/WCH2-W090", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:2369", "collection": "thesis", "collection_id": "2369", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06012009-021047", "primary_object_url": { "basename": "Full_Thesis.pdf", "content": "final", "filesize": 18582537, "license": "other", "mime_type": "", "url": "/2369/3/Full_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Nonlinear Electrical Properties of One-Dimensional Nanostructures", "author": [ { "family_name": "Xu", "given_name": "Ke", "orcid": "0000-0002-2788-194X", "clpid": "Xu-Ke" } ], "thesis_advisor": [ { "family_name": "Heath", "given_name": "James R.", "clpid": "Heath-J-R" } ], "thesis_committee": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Heath", "given_name": "James R.", "clpid": "Heath-J-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A general method is first reported for reliably fabricating highly-ordered conventional superconductor nanowire arrays, with good control over nanowire cross section (down to 10 nm by 11 nm) and length (up to 200 microns). Nanowire size effects are systematically studied through electrical measurements and explained with theories. A comprehensive investigation of influence of nanowire length on superconductivity is reported for the first time.
\r\n\r\nWe further demonstrate the preparation and electrical properties of high-temperature superconductor nanowires. We find that high-temperature superconductivity can be retained in nanowires ~10 nm in width and >100 microns in length. All nanowires exhibit a superconducting transition above liquid nitrogen temperature, and a transition temperature width that depends strongly upon the nanowire dimensions.
\r\n\r\nThe experience gained from the above projects has allowed for the fabrication of superconductor films patterned with ultrahigh-density (pitch ~30 nm) two-dimensional arrays of nano-holes. Significantly enhanced critical currents are observed in such systems.
\r\n\r\nWe then describe a method for the assembly of nanoparticles into granular solids that can be tuned continuously from two dimensions to one dimension, and establish how electron transport evolves between these limits. We find that the energy barriers to transport increase in the one-dimensional limit, in both the variable-range-hopping and sequential-tunneling regimes. Furthermore, in the sequential-tunneling regime, we find an unexpected relationship that is peculiar to one-dimensional systems, between the temperature and the voltage at which the conductance becomes appreciable. These results are explained by extrapolating existing theories to one dimension.
\r\n\r\nWe also describe an approach to combine the geometric confinement of a Si nanowire and the electric field confinement from an array of ultrahigh-density top gates to form a concatenated array of coupled quantum dots. Reproducible confinement and coupling effects are observed.
\r\n\r\nWe have achieved single-atomic resolution in our scanning tunneling microscopy studies of graphene sheets on SiO2 substrates, from which we discovered significant changes in electronic states for bended regions in graphene sheets. We have also carried out the first systematic study on local conductance variations in graphene. Our results suggest large local variations in both the morphology and the electrical properties of graphene.
\r\n", "doi": "10.7907/BPK0-3V37", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:2169", "collection": "thesis", "collection_id": "2169", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05272008-095638", "primary_object_url": { "basename": "jasonkeith_thesis_final.pdf", "content": "final", "filesize": 2467428, "license": "other", "mime_type": "application/pdf", "url": "/2169/1/jasonkeith_thesis_final.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Palladium Mediated Activation of Molecular Oxygen", "author": [ { "family_name": "Keith", "given_name": "Jason M.", "orcid": "0000-0002-5292-397X", "clpid": "Keith-Jason-M" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In developing environmentally benign chemistries, it is most important to use dioxygen directly in lieu of toxic and/or corrosive stoichiometric oxidants. Unfortunately, for many processes such as direct oxidations this has not yet become practical. To help develop such processes, we elucidate here the mechanism for the reaction of molecular oxygen with palladium-hydride complexes in nonpolar solvent using quantum mechanics for several PdII complexes, specifically focusing on the pathways proceeding through Pd0 and on the direct insertion of oxygen into the Pd-H bond. All the chapters presented herein focus on different aspects of the total problem as follows:
\r\n\r\nChapter 1: Activation of Molecular Oxygen by ((\u2012)-Sparteine)PdHCl: Direct Insertion presents the first proposal of a hydrogen atom abstraction from a palladium-hydride complex by triplet oxygen that demonstrates the feasibility of this mechanism.
\r\n\r\nChapter 2: Activation of Molecular Oxygen by [1,3-(CH2PtBu2)2-C6H3]PdH examines the reaction of an experimentally isolated palladium-hydride complex from which formation of Pd0 has been deemed unlikely, thus proving the previously predicted insertion mechanism to be active in a known system.
\r\n\r\nChapter 3: Activation of Molecular Oxygen by ((\u2012)-Sparteine)PdHCl: Pd0 presents a thorough investigation of possible base-assisted reductive elimination pathways that can lead to the formation of Pd0 in the ((\u2012)-Sparteine)PdHCl system, and it demonstrates that the direct insertion mechanism is in fact the process involved in this system.
\r\n\r\nChapter 4: Activation of Molecular Oxygen by ((\u2012)-Sparteine)Pd(OAc)H: Pd0 vs. Direct Insertion examines the substitution of the OAc ion for Cl in ((\u2012)-Sparteine)PdH system. The acetate ligand\u2019s ability to act as a base while chelating the Pd significantly lowers the energy involved in the Pd0 pathway, switching the calculated preference to the Pd0 pathway.
\r\n\r\nChapter 5: Activation of Molecular Oxygen by (Pyridine)2Pd(OAc)H: Pd0 vs. Direct Insertion examines the reaction of (Pyridine)2Pd(OAc)H with O2. The calculated mechanisms present feasible cis/trans isomerisation and demonstrate that the Pd0 pathway is the favored pathway for both the cis and the trans cases.
\r\n\r\nAppendix: Enantioselective Oxidations of Secondary Alcohols by (\u2013)-Sparteine-PdII Complexes examines the mechanism of specific Pd oxidation catalysis focusing on alcohol binding, deprotonation to form the corresponding alkoxide and the subsequent beta-hydride elimination.
\r\n", "doi": "10.7907/K4AY-P498", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:5234", "collection": "thesis", "collection_id": "5234", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06112008-065533", "primary_object_url": { "basename": "10Thesis.pdf", "content": "final", "filesize": 1432379, "license": "other", "mime_type": "application/pdf", "url": "/5234/11/10Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Novel Methods for Force-Detected Nuclear Magnetic Resonance", "author": [ { "family_name": "Butler", "given_name": "Mark Cheiron", "clpid": "Butler-Mark-Cheiron" } ], "thesis_advisor": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" } ], "thesis_committee": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" }, { "family_name": "Shan", "given_name": "Shu-ou", "clpid": "Shan-Shu-ou" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis is concerned with the problem of extending methods for force-detected nuclear magnetic resonance (NMR) to the nanoscale regime. A magnetic mechanical resonator can be used both as a sensitive detector of spins and a means of inducing spin relaxation between detected transients. At the mK temperatures achievable in a dilution refrigerator, spin-lattice interactions are \"frozen out,\" and resonator-induced relaxation can replace spin-lattice relaxation in returning the spins to equilibrium between detected transients. We analyze resonator-induced spin relaxation and the sensitivity of schemes which use a nanoscale mechanical resonator to detect spins.
\r\n\r\nRelaxation equations are derived from first principles, and a physical interpretation of the processes contributing to resonator-induced relaxation is given. The intrinsically quantum mechanical nature of the relaxation is highlighted by comparing the quantum mechanical relaxation equations with analogous equations derived using a semiclassical model in which all spin components have a definite value simultaneously. In the case where the spins all experience the same field, the semiclassical spins cannot become polarized as a result of their interaction with the resonator, and a quantum mechanical model is necessary even for a qualitative description of the polarization process.
\r\n\r\nResonator-induced relaxation of spin systems is complicated by the fact that an indirect spin-spin interaction is present when all spins are coupled to the same resonator, since the resonator's field at a given spin is determined by the interactions which have occurred between the resonator and the other spins of the system. This indirect interaction can prevent the spins from relaxing to a thermal state characterized by a spin temperature. We present a physical interpretation of the mechanism by which an indirect spin-spin torque develops during resonator-induced relaxation, and we estimate the magnitude of this torque and the time T_corr required for it to induce strong spin-spin correlations. A perturbation in the spin Hamiltonian which periodically reverses the direction of the indirect torques within a time period shorter than T_corr will prevent the development of resonator-induced correlations and allow the spins to relax to a thermal state.
\r\n\r\nThe mechanisms by which the spin Hamiltonian H_s modifies resonator-induced relaxation are characterized. In the case where the eigenstates of H_s are weakly perturbed from product states, the system will relax exponentially to thermal equilibrium with the resonator, provided that resonator-induced couplings between populations and certain zero-quantum coherences are suppressed by terms in H_s which shift the frequencies of these coherences sufficiently far from zero. Analysis of longitudinal relaxation in example systems containing three dipole-dipole coupled spins shows that the relaxation occurs in two stages governed by different physical processes, and the three-spin systems do not relax to a thermal state. For substantially larger dipole-dipole coupled system (e.g., N = 50), we propose the hypotheses that the secular dipolar Hamiltonian will quickly equalize the population of states which lie in the same eigenspace of I_z. Simulations of the longitudinal relaxation predicted by this hypothesis suggest that a single resonator could efficiently relax dipole-dipole coupled systems to a thermal state.
\r\n\r\nArguments based on general properties of the master equation suggest that the transverse relaxation induced by the mechanical resonator could occur on a shorter time scale than that of the longitudinal relaxation. We derive conditions which guarantee that the time constant for transverse relaxation will be 2/R_h, where 1/R_h is the time constant for resonator-induced longitudinal relaxation of a single-spin sample to thermal equilibrium. Under these conditions, transverse relaxation can be interpreted as the \"lifetime broadening\" associated with the shortened lifetime of energy eigenstates due to coupling with the resonator. For a two-spin system, however, we show analytically that \"turning on\" the dipolar coupling can accelerate resonator-induced transverse relaxation, and we give an interpretation of the mechanism by which this occurs. Simulations of four-spin systems also show that the presence of dipolar couplings can substantially accelerate resonator-induced transverse relaxation, and that this accelerated relaxation can be distinguished from so-called radiation damping. In addition, we find that spin-locking limits the rate of resonator-induced transverse relaxation. In the case where the spin-locking field is large enough to average the dipolar Hamiltonian and the superoperator responsible for resonator-induced relaxation, we have T_1rho = 2/R_h.
\r\n\r\nWe propose a general definition of signal-to-noise ratio (SNR) which can be used to compare the sensitivity of methods that measure the amplitude of a signal with the sensitivity of methods that yield a continuous record of a signal. This definition is used to compare the sensitivity of three schemes for detecting the NMR signal of a sample consisting of a few spins: spin-locked detection of a transverse dipole, detection of a freely-precessing dipole, and detection of a correlated product. The dependence of SNR and acquisition time on resonator parameters is analyzed. We find that when the time constant for decay of the signal during the detection period is 2/R_h, with instrument noise substantially larger than spin noise, the only resonator parameter which appears in the SNR expressions is the ratio of the mechanical frequency to the temperature. This result suggests, in particular, that SNR for spin-locked detection will be insensitive to details of resonator design.
\r\n\r\nA torsional mechanical resonator design is presented. We discuss the advantages of using soft magnetic material and eliminating relative motion between the sample and the resonator, as well as the validity of the models used to characterize the resonator. The possibility of using non-metallic magnetic material as the source of the resonator's magnetic field is introduced. A numerical example is presented for which the calculated time constant for the longitudinal relaxation of a single-spin sample is 1/R_h = 0.77 s. Simulations of detected NMR spectra for two-spin samples suggest the possibility of chemical studies in which force-detected NMR spectroscopy is used with single-spin sensitivity.
\r\n\r\nThe final chapter studies the possibility of using hyperpolarized spins to cool a single mechanical mode. Numerical examples suggest that cooling would be negligible for resonators of size scale ~ 10 um or larger. In the regime characterized by these examples, substantial cooling requires sufficiently strong spin-resonator coupling that neither a mechanical mode nor a spin mode can be distinguished in the spin-resonator system; instead, the modes of the system include equal contributions from the spins and the mechanical resonator. The spin-resonator correlations responsible for cooling make a significant contribution to the symmetric correlation function of the resonator coordinate, with the result that the noisy \"thermal torque\" acting on the resonator is increased rather than diminished by the presence of the hyperpolarized spins.
\r\n", "doi": "10.7907/S5K2-NH54", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:5223", "collection": "thesis", "collection_id": "5223", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06062008-171210", "primary_object_url": { "basename": "KGrubitsThesis.pdf", "content": "final", "filesize": 18814044, "license": "other", "mime_type": "application/pdf", "url": "/5223/1/KGrubitsThesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Low-Dimensional Representations of Transitions in Molecular Systems", "author": [ { "family_name": "Grubits", "given_name": "Katalin Anna", "clpid": "Grubits-Katalin-Anna" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Owhadi", "given_name": "Houman", "clpid": "Owhadi-H" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A major difficulty in modeling molecular systems is that the number of dimensions, even for a small system, is commonly too large for computation to be feasible. To overcome this challenge, a combination of lower-dimensional representations of the system and improved computational methods are required. In this thesis, we investigate techniques to achieve both of these aims via three model problems.
\r\n\r\nBy exploiting an understanding of the mechanism and dynamics of reaction in the systems considered, we attain a low-dimensional description of the transition that captures the essential dynamics. For the ionization of a Rydberg atom we utilize concepts from dynamical systems theory that reveal the geometric structures in phase space that mediate the reaction. The gyration radius formalism captures the kinematic effects of the secondary particles in a coarse variable that reduces the number of dimensions of the model, thereby providing a simple description of our methane and oxygen dissociation example. These methods are applicable more generally and provide a coarse model of chemical reactions that can be combined with efficient computational tools, such as the set-oriented method employed in our Rydberg example, to efficiently compute reaction rates of previously difficult problems.
\r\n\r\nThe third model problem considered is the self-assembly of particles into an ordered lattice configuration under the influence of an isotropic inter-particle potential. With the aim of characterizing the transition from a disordered to an ordered state, we develop metrics that assess the quality of the lattice with respect to the target lattice configuration. The five metrics presented use a single number to quantify the order within this large system of particles. We explore numerous applications of these quality assessment tools, in particular, finding the optimal potential for self-assembly. The very noisy, highly variable nature of our expensive-to-evaluate objective function prompted the development of a trend optimization algorithm that efficiently minimizes the objective function, using upper and lower envelopes that are responsible for the robustness of the method and the solution. This trend optimization scheme is widely applicable to problems in other fields.
", "doi": "10.7907/YMTC-WQ16", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:534", "collection": "thesis", "collection_id": "534", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02072005-173741", "primary_object_url": { "basename": "pintgen_PhD.pdf", "content": "final", "filesize": 47771543, "license": "other", "mime_type": "application/pdf", "url": "/534/1/pintgen_PhD.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Detonation Diffraction in Mixtures with Various Degrees of Instability", "author": [ { "family_name": "Pintgen", "given_name": "Florian Peter", "clpid": "Pintgen-Florian-Peter" } ], "thesis_advisor": [ { "family_name": "Shepherd", "given_name": "Joseph E.", "clpid": "Shepherd-J-E" } ], "thesis_committee": [ { "family_name": "Shepherd", "given_name": "Joseph E.", "clpid": "Shepherd-J-E" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Hornung", "given_name": "Hans G.", "clpid": "Hornung-H-G" }, { "family_name": "Beck", "given_name": "James L.", "clpid": "Beck-J-L" }, { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" } ], "local_group": [ { "literal": "Explosion Dynamics Laboratory" }, { "literal": "div_eng" } ], "abstract": "Planar laser induced fluorescence (PLIF) is widely used in combustion diagnostics but has only recently been successfully applied to detonation. The strong spatial variations in temperature, pressure, and background composition under these conditions influence the quantitative link between OH-number density and fluorescence intensity seen on images. Up to now, this has lead to uncertainties in interpreting the features seen on PLIF images obtained in detonations. A one-dimensional fluorescence model has been developed, which takes into account light sheet attenuation by absorption, collisional quenching, and changing absorption line shape. The model predicts the fluorescence profile based on a one-dimensional distribution in pressure, temperature, and mixture composition. The fluorescence profiles based on a calculated ZND detonation profile were found to be in good agreement with experiments.
\r\n\r\nThe PLIF technique is used to study the diffraction process of a self-sustained detonation wave into an unconfined space through an abrupt area change. Simultaneous schlieren images enable direct comparison of shock and reaction fronts. Two mixture types of different effective activation energy [theta] are studied in detail, these represent extreme cases in the classification of detonation front instability and cellular regularity. Striking differences are seen in the failure mechanisms for the very regular H2-O2-Ar mixture ([theta] ~ 4.5) and the highly irregular H2-N2O mixture ([theta] ~ 9.4). Detailed image analysis quantifies the observed differences. Stereoscopic imaging reveals the complex three-dimensional structure of the transverse detonation and its location with respect to the shock front. The study is concluded by using the experimentally-obtained shock and reaction front profiles in a simplified model to examine the decoupling of the shock from the chemical reaction. The rapid increase in activation energy for the H2-O2-Ar mixtures with decreasing shock velocity is proposed as an important new element in the analysis of diffraction for these mixture.
", "doi": "10.7907/YSG0-TH85", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:4822", "collection": "thesis", "collection_id": "4822", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12072004-021118", "primary_object_url": { "basename": "YouyongLi_Thesis.pdf", "content": "final", "filesize": 3996304, "license": "other", "mime_type": "application/pdf", "url": "/4822/1/YouyongLi_Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Atomistic Simulation of Macromolecules", "author": [ { "family_name": "Li", "given_name": "Youyong", "orcid": "0000-0002-5248-2756", "clpid": "Li-Youyong" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Grubbs", "given_name": "Robert H.", "clpid": "Grubbs-R-H" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis focuses on the atomistic simulation of polymers/dendrimers material properties and development/applications of Monte Carlo methods for macromolecules. The main topics and their outlines are listed as following.
\r\n\r\n1) Structures and properties of crystalline polymers from theory. Although crystalline polymers such as nylon are important industrial materials, it is difficult to get the details of the various structures/properties and the conversion between them from the experiment. Using molecular modeling, we successfully predicted the complicated structures/properties and illustrated the process of forming the polymer crystal and conversion mechanism among those structures.
\r\n\r\n2) Packing mechanism of self-assembly dendrimer balls with soft coronas. Using the vibrational density of state (DoS) derived from molecular dynamic simulations, we investigate the free energy of the liquid crystal formed by soft dendrimer balls. We find that the preferred lattice for soft balls is different from the hard balls and illustrate the mechanism.
\r\n\r\n3) Development of CCBTX Monte Carlo method for polymer and dendrimer. Although computer simulation has developed as a powerful research tool to study polymer/dendrimer materials properties recently, it has been hampered by the difficulties of sampling amorphous polymer/dendrimer configurations efficiently. We develop the efficient Continuous Configurational Biased TX (CCBTX) method to generate high-quality amorphous polymer and dendrimer atomistic structures directly. The code is implemented in C++ and ported in python environment, which provides friendly interface.
\r\n\r\n4) Thermodynamic functions, critical exponents, and theta temperatures of polymer chains from CCBB Monte Carlo method. We examine the thermodynamic properties (entropy, energy, end-to-end distance) of isolated polymer chains with the Monte Carlo method.
", "doi": "10.7907/NW1Q-1E81", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2004", "collection": "thesis", "collection_id": "2004", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-165713", "primary_object_url": { "basename": "Bergthorson_JM_2005_thesis.pdf", "content": "final", "filesize": 4951106, "license": "other", "mime_type": "application/pdf", "url": "/2004/6/Bergthorson_JM_2005_thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Experiments and Modeling of Impinging Jets and Premixed Hydrocarbon Stagnation Flames", "author": [ { "family_name": "Bergthorson", "given_name": "Jeffrey Myles", "orcid": "0000-0003-2924-7317", "clpid": "Bergthorson-Jeffrey-Myles" } ], "thesis_advisor": [ { "family_name": "Dimotakis", "given_name": "Paul E.", "clpid": "Dimotakis-P-E" } ], "thesis_committee": [ { "family_name": "Dimotakis", "given_name": "Paul E.", "clpid": "Dimotakis-P-E" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Meiron", "given_name": "Daniel I.", "clpid": "Meiron-D-I" }, { "family_name": "Goodwin", "given_name": "David G.", "clpid": "Goodwin-D-G" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "clpid": "Shepherd-J-E" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "To model the combustion of long-chain hydrocarbon fuels, an accurate kinetics mechanism must first be developed for the oxidation of small hydrocarbons, such as methane, ethane, and ethylene. Even for methane, a generally accepted mechanism is still elusive due to a lack of kinetically independent experimental data. In this work, a combined experimental and modeling technique is developed to validate and further optimize these mechanisms. This technique relies on detailed measurements of strained flames in a jet-wall stagnation flow using simultaneous Particle Streak Velocimetry (PSV) and CH Planar Laser Induced Fluorescence (PLIF). Stagnation flames are simulated using an axisymmetric, one-dimensional model with accurate specification of the requisite boundary conditions. Direct comparisons between experiment and simulation allow for an assessment of the various models employed, with an emphasis on the chemistry model performance.
\r\n\r\nThe flow field for a cold impinging laminar jet is found to be independent of the nozzle-to-plate separation distance if velocities are scaled by the Bernoulli velocity. The one-dimensional formulation is found to accurately model the stagnation flow if the velocity boundary conditions are appropriately specified. The boundary-layer-displacement-thickness corrected diameter is found to be an appropriate scale for axial distances and allows the identification of an empirical, analytical expression for the flow field of the impinging laminar jet.
\r\n\r\nStrained methane-air flame experiments confirm that the reacting flow is also independent of the nozzle-to-plate separation distance. Methane, ethane, and ethylene flames are studied as functions of the applied strain rate, mixture dilution, and mixture fraction. Mechanism performance is found to be relatively insensitive to both the mixture dilution and the imposed strain rate, while exhibiting a stronger dependence on the fuel type and flame stoichiometry. The approach and diagnostics presented here permit an assessment of the predictions of strained-hydrocarbon flames for several combustion chemistry mechanisms. The data presented in this thesis are made available to kineticists looking for optimization targets, with the goal of developing a predictive kinetics model for hydrocarbon fuels. The methodology described here can allow new optimization targets to be rapidly measured, reducing the experimental burden required to fully constrain the chemistry models.
", "doi": "10.7907/7FQZ-EY88", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2196", "collection": "thesis", "collection_id": "2196", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-161503", "primary_object_url": { "basename": "Thesis.pdf", "content": "final", "filesize": 13394896, "license": "other", "mime_type": "application/pdf", "url": "/2196/1/Thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Computation Aided Design in Molecular Nanotechnology", "author": [ { "family_name": "Deng", "given_name": "Wei-Qiao", "orcid": "0000-0002-3671-5951", "clpid": "Deng-Wei-Qiao" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Goodwin", "given_name": "David G.", "clpid": "Goodwin-D-G" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "We use multi-scale simulation strategy to understand, improve and rationally design novel materials with desired properties in molecular nanotechnology. The areas we have studied cover from molecular electronics, nano-structured materials to carbon nanotube technology.
\r\n\r\nIn term of molecular and nano-electronics, first we used quantum mechanics to characterize the structure and current-voltage (I-V) performance of the Stoddart-Heath rotaxane-based programmable electronic switch. This methodology established a basis for iterative experimental-theoretical efforts to optimize systems for molecule-based electronics. We extended this switch principle and rationally designed an ultrafast molecular switch, proton-hopping molecular switch. Second we developed a kinetic model to study the hole mobility in organic semiconductor. After screening several designs, we presented a nano-bracelet as a competitive organic semiconductor.
\r\n\r\nWe studied several topics related to the applications of nano-structured materials in fuel cell technology. Based on our simulation, we proposed a new kind of carbon-based materials for hydrogen storage. It can satisfy the target set up by the Department of Energy, USA. We develop a kinetic model to study the proton diffusion in proton exchange membrane of hydrogen fuel cell. We validated our proposed system, fluorinated imidazole impregnated nafion, as the candidate that can transfer proton above 100 0C at water-free media.
\r\n\r\nIn term of carbon nanotube technology, we explored the reason why bimetallic catalysts are 10-100 times better than mono-metals at assisting single wall carbon nanotube growth. Based on our proposed two-stage growth mechanism, we screened and designed a better catalysis.
", "doi": "10.7907/3EKY-3J53", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" }, { "id": "thesis:4784", "collection": "thesis", "collection_id": "4784", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12052002-203732", "primary_object_url": { "basename": "abrol_thesis.pdf", "content": "final", "filesize": 5516234, "license": "other", "mime_type": "application/pdf", "url": "/4784/1/abrol_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Theory of Electronically Nonadiabatic Quantum Reaction Dynamics", "author": [ { "family_name": "Abrol", "given_name": "Ravinder", "orcid": "0000-0001-7333-6793", "clpid": "Abrol-Ravinder" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In most quantum descriptions of chemical reactions, the Born-Oppenheimer (BO) approximation is invoked that separates the motion of light electrons and heavy nuclei, thereby restricting the motion of those nuclei to a single adiabatic electronic state. Intersections between neighboring electronic states are more common in molecular systems of interest to chemistry and biology than in diatomic molecules. The picture is further complicated due to nonadiabatic couplings which can be present in these systems even in the absence of intersections between electronic states. These couplings are solely responsible for all nonadiabatic effects in chemical and biological processes. For understanding these nonadiabatic effects, the BO picture needs to be replaced by the general Born-Huang (BH) description, in which the nuclei can sample an arbitrary number of electronic states.
\r\n\r\nA general BH treatment is presented for a polyatomic system evolving on n adiabatic electronic states. All nonadiabatic couplings are considered in this adiabatic representation. These couplings can be singular for electronically degenerate nuclear geometries. The presence of these nonadiabatic couplings (even if not singular) can lead to numerical inefficiencies in the solution of the corresponding nuclear motion Schr\"odinger equation. This problem is circumvented by going to a diabatic representation, in which these couplings are not only never singular but are also minimized over the entire dynamically important nuclear configuration space. This BH description is applied to the benchmark triatomic system H\u2083 by obtaining an optimal diabatic representation of its lowest two adiabatic electronic states. A two-electronic-state quantum dynamics formulation is also presented, which, in addition to providing reaction cross sections over a broad energy range, will also enable a quantitative test of the validity of the BO approximation.
", "doi": "10.7907/6NQY-2K60", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:1004", "collection": "thesis", "collection_id": "1004", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03192003-095722", "type": "thesis", "title": "Electron Transfer at Metal Surfaces", "author": [ { "family_name": "Gosavi", "given_name": "Shachi Sharadchandra", "orcid": "0000-0001-7219-8333", "clpid": "Gosavi-Shachi-Sharadchandra" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In recent years there has been considerable interest in electrode processes at metal surfaces with alkanethiol monolayers attached to them. One effect of the monolayer is that the electron transfer rate from the redox reagent in solution to the metal (gold or platinum are commonly used) becomes clearly nonadiabatic and the effect of the density of states of the metal on such a rate can be investigated.
\r\n\r\nWe develop a way of writing the wave function of a semi-infinite metal using tight-binding matrix elements and the 'Z-transform', a discrete Laplace transform. Using these k-dependent metal wave functions we calculate the coupling matrix element between the metal and the redox reagent and thus the electron transfer rate constant. We then study the effect of changing the density of electronic states at the Fermi level (DOS) of a metal on the rate of nonadiabatic electron transfer by changing the metal.
\r\n\r\nThe DOS of platinum is about 7.5 times that of gold, the difference being mainly due to the d-band of Pt. Inspite of this difference, the calculated electron transfer rate constant increases only by a factor of about 1.8. Bands which are weakly coupled (e.g., the d-band of Pt in the present case) contribute much less to the rate constant than is suggested by their density of states. Thereby, the rate constant is approximately independent of the density of states in two cases: adiabatic electron transfer and nonadiabatic electron transfer when the extra density of states is due to weakly coupled bands. Our results are in agreement with experiments performed with systems similar to those used in our calculations.
\r\n\r\nWe next employ our method to calculate the temperature dependence of the electronic contribution to the nonadiabatic electron transfer rate constant at metal and semiconductor electrodes. We find that the electronic contribution in metals is proportional to T, and under conditions for the maximum rate constant, that at semiconductor electrodes is also proportional to T, but for different reasons than in the case of metals (Boltzmann statistics and transfer at the conduction band edge for the semiconductor vs. Fermi-Dirac statistics and transfer at the Fermi level, which is far from the band edge, of the metal).
\r\n \r\nOn a different topic, we study the inverse photoemission spectra at metal electrode-liquid interfaces. In such experiments, an electron transfer redox agent was used to inject electrons or holes into a metal and create excited electronic states of the metal. Emission thus occurs in competition with energy loss and radiationless transitions. Some of the excited states decay radiatively and gave a frequency-dependent spectrum. The spectrum may be analysed to probe the electronic structure of the metal above and below its Fermi level. The experimental technique, known in the literature as charge transfer inverse photoemission spectroscopy (CTRIPS), is treated theoretically here.
\r\n\r\nWe give a possible explanation of the data using a model, experimental band structures (from vacuum inverse photemission) and surface states from solution electroreflectance (ER) experiments and propose experiments that could be performed to further clarify the mechanism of electron transfer.
", "doi": "10.7907/KK8A-ZF26", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:5036", "collection": "thesis", "collection_id": "5036", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12182002-190040", "primary_object_url": { "basename": "zhangdq-thesis.pdf", "content": "final", "filesize": 6745389, "license": "other", "mime_type": "application/pdf", "url": "/5036/1/zhangdq-thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Structure-Based Design of Mutant Proteins: I. Molecular Docking Studies of Amino Acid Binding to Wild-Type Aminoacyl-tRNA Synthetases. II. Structure-Based Design of Mutant Aminoacyl-tRNA Synthetases for Non-Natural Amino Acid Incorporation", "author": [ { "family_name": "Zhang", "given_name": "Deqiang", "clpid": "Zhang-Deqiang" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Roberts", "given_name": "Richard W.", "clpid": "Roberts-R-W" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Chan", "given_name": "Sunney I.", "clpid": "Chan-S-I" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Protein biosynthesis has precisely controlled accuracy, and aminoacyl-tRNA synthetases (AARSs) play an important role in charging amino acids to their cognate tRNAs with high fidelity. In some cases the misactivation of non-natural amino acids by the wild-type or mutant AARS can be utilized to incorporate these non-natural amino acids into proteins in vivo. Such technique has tremendous potentials in protein engineering and other applications. Therefore, it is essential to understand the amino acid recognition mechanism displayed by AARSs.
\r\n\r\nIn this thesis, computational studies of the selection of natural and non-natural amino acids by AARSs at the binding stage have been conducted for methionyl-tRNA synthetase (Chapter 2), histidyl-tRNA synthetases (Chapter 3), and isoleucyl-tRNA synthetase (Chapter 4). In these chapters, molecular docking and ligand perturbation are used to elucidate the binding discrimination showed by these AARSs.
\r\n\r\nBecause many non-natural amino acids carrying interesting physical and chemical properties on their side chains cannot be incorporated by using the wild-type AARSs, it is necessary to manipulate the activity of AARSs by making mutations in the binding site of amino acids. To this end, we have developed a Clash Opportunity Progressive (COP) protein design tool to redesign the binding site of AARSs. Chapter 5 describes the main steps in COP. Chapters 6 to 8 present the application of COP to different AARSs. In Chapter 6, COP has been applied to design mutant tyrosyl-tRNA synthetase (TyrRS) for recognizing Ome-Tyr, Naph-Ala, and p-keto-Tyr. In Chapter 7, COP has been used to design mutant phenylalanyl-tRNA synthetase for p-keto-Phe. In Chapter 8, tryptophanyl-tRNA synthetase is used as a template to design mutant AARS to recognize NBD-Ala, bpy-Ala, and DAN-Ala.
\r\n\r\nThe appendices are some publications and manuscripts on various other projects. Appendix I is a molecular dynamics study of laboratory-evolved pNBE enzymes with different thermostability. The findings presented here will help us to better understand the determinants in protein stability evolution. Appendix II contains experimental work I have done in the Chan group. Unfolding experiments revealed the existence of intermediates in the equilibration unfolding of RdPf. In Appendix III, femtosecond time-resolved spectroscopy was used to study the fluorescence resonance energy transfer and tryptophan solvation dynamics in RdPf.
", "doi": "10.7907/CN3G-JH45", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:6777", "collection": "thesis", "collection_id": "6777", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01252012-135136531", "primary_object_url": { "basename": "Feldmann_mt_2002.pdf", "content": "final", "filesize": 53221379, "license": "other", "mime_type": "application/pdf", "url": "/6777/1/Feldmann_mt_2002.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Quantum Monte Carlo: Quest to Get Bigger, Faster, and Cheaper", "author": [ { "family_name": "Feldmann", "given_name": "Michael Todd", "clpid": "Feldmann-Michael-Todd" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Bruck", "given_name": "Jehoshua", "orcid": "0000-0001-8474-0812", "clpid": "Bruck-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Pierce", "given_name": "Niles A.", "orcid": "0000-0003-2367-4406", "clpid": "Pierce-N-A" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "We reexamine some fundamental Quantum Monte Carlo (QMC) algorithms with the goal of making QMC more mainstream and efficient. Two major themes exist: (1) Make QMC faster and cheaper, and (2) Make QMC more robust and easier to use. A fast \"on-the-fly\" algorithm to extract uncorrelated estimators from serially correlated data on a huge network is presented, DDDA. A very efficient manager-worker algorithm for QMC parallelization is presented, QMC-MW. Reduced expense VMC optimization procedure is presented to better guess initial Jast row parameter sets for hydrocarbons, GJ. I also examine the formation and decomposition of aminomethanol using a variety of methods including a test of the hydrocarbon GJ set on these oxygen- and nitrogen-containing systems. The QMC program suite QMcBeaver is available from the authors in its entirety while a user's and developer's manual is attached as supplementary material.", "doi": "10.7907/4D4F-WZ34", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:8146", "collection": "thesis", "collection_id": "8146", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03192014-125137237", "primary_object_url": { "basename": "Gao-yq-2001.pdf", "content": "final", "filesize": 30151528, "license": "other", "mime_type": "application/pdf", "url": "/8146/1/Gao-yq-2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Theory of Ozone Isotopic Effects and Various Electron Transfer Reaction", "author": [ { "family_name": "Gao", "given_name": "Yi Qin", "clpid": "Gao-Yi-Qin" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Three separate topics, each stimulated by experiments, are treated theoretically in this dessertation: isotopic effects of ozone, electron transfer at interfaces, and intramolecular directional electron transfer in a supramolecular system.
\r\n\r\nThe strange mass-independent isotope effect for the enrichment of ozone, which has been a puzzle in the literature for some 20 years, and the equally puzzling unconventional strong mass-dependent effect of individual reaction rate constants are studied as different aspects of a symmetry-driven behavior. A statistical (RRKM-based) theory with a hindered-rotor transition state is used. The individual rate constant ratios of recombination reactions at low pressures are calculated using the theory involving (1) small deviation from the statistical density of states for symmetric isotopomers, and (2) weak collisions for deactivation of the vibrationally excited ozone molecules. The weak collision and partitioning among exit channels play major roles in producing the large unconventional isotope effect in \"unscrambled\" systems. The enrichment studies reflect instead the non-statistical effect in \"scrambled\" systems. The theoretical results of low-pressure ozone enrichments and individual rate constant ratios obtained from these calculations are consistent with the corresponding experimental results. The isotopic exchange rate constant for the reaction ^(16)O + ^(18)O ^(18)O\u2192+ ^(16)O ^(18)O + ^(18)O provides information on the nature of a variationally determined hindered-rotor transition state using experimental data at 130 K and 300 K. Pressure effects on the recombination rate constant, on the individual rate constant ratios and on the enrichments are also investigated. The theoretical results are consistent with the experimental data. The temperature dependence of the enrichment and rate constant ratios is also discussed, and experimental tests are suggested. The desirability of a more accurate potential energy surface for ozone in the transition state region is also noted.
\r\n\r\nElectron transfer reactions at semiconductor /liquid interfaces are studied using a tight-binding model for the semiconductors. The slab method and a z-transform\r\nmethod are employed in obtaining the tight-binding electronic structures of semiconductors having surfaces. The maximum electron transfer rate constants at Si/viologen^(2-/+) and InP /Me_(2)Fc^(+/O) interfaces are computed using the tight-binding type calculations for the solid and the extended-Huckel for the coupling to the redox agent at the interface. These electron transfer reactions are also studied using a free electron model for the semiconductor and the redox molecule, where Bardeen's method is adapted to calculate the coupling matrix element between the molecular and semiconductor electronic states. The calculated results for maximum rate constant of the electron transfer from the semiconductor bulk states are compared with the experimentally measured values of Lewis and coworkers, and are in reasonable agreement, without adjusting parameters. In the case of InP /liquid interface, the unusual current vs applied potential behavior is additionally interpreted, in part, by the presence of surface states.
\r\n\r\nPhotoinduced electron transfer reactions in small supramolecular systems, such as 4-aminonaphthalimide compounds, are interesting in that there are, in principle,\r\ntwo alternative pathways (directions) for the electron transfer. The electron transfer, however, is unidirectional, as deduced from pH-dependent fluorescence quenching studies on different compounds. The role of electronic coupling matrix element and the charges in protonation are considered to explain the directionality of the electron transfer and other various results. A related mechanism is proposed to interpret the fluorescence behavior of similar molecules as fluorescent sensors of metal ions.
\r\n", "doi": "10.7907/fj7v-ht75", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:3255", "collection": "thesis", "collection_id": "3255", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08282001-123851", "primary_object_url": { "basename": "JGK_Thesis_for_DBLsided_printing.pdf", "content": "final", "filesize": 3984594, "license": "other", "mime_type": "application/pdf", "url": "/3255/1/JGK_Thesis_for_DBLsided_printing.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Probing Quantum Confinement at the Atomic Scale with Optically Detected Nuclear Magnetic Resonance", "author": [ { "family_name": "Kempf", "given_name": "James G.", "clpid": "Kempf-James-G" } ], "thesis_advisor": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "orcid": "0000-0003-0079-8000", "clpid": "Weitekamp-D-P" } ], "thesis_committee": [ { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "orcid": "0000-0003-0079-8000", "clpid": "Weitekamp-D-P" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Near-band-gap circularly polarized excitation in III-V semiconductors provides spin-polarized electrons that transfer spin order to lattice nuclei via fluctuations in the contact hyperfine interaction. This process of optical nuclear polarization and the complementary technique of optical detection of nuclear magnetic resonance (NMR) provide extreme sensitivity enhancement and spatial selectivity in structured samples, enabling collection of NMR spectra from samples such as single quantum wells or dots containing as few as ~10^5 nuclei.
\r\n\r\nCombining these advances with novel techniques for high spectral resolution, we have probed quantum-confined electronic states near the interface of a single epitaxially grown Al(1-x)Ga(x)As/GaAs (x = 0.36) heterojunction. Using a novel strategy that we refer to as POWER (perturbations observed with enhanced resolution) NMR, multiple-pulse time suspension is synchronized with bandgap optical irradiation to reveal spectra of effective spin Hamiltonians that are differences between those of the occupied and unoccupied photoexcited electronic state. The underlying NMR linewidth is reduced by three orders of magnitude in these experiments, enabling resolution of an asymmetric line shape due to light-induced hyperfine interactions. The results are successfully fit with the coherent nuclear spin evolution and relaxation theoretically expected for sites distributed over the volume of an electronic excitation weakly localized at a point defect. This analysis establishes a one-to-one relationship, which can be used to follow nuclear spin diffusion, between optical Knight shift and the radial position of lattice nuclei.
\r\n\r\nWe have also introduced POWER NMR techniques to characterize the change in electric field associated with cycling from light-on to light-off states via a linear quadrupole Stark effect (LQSE) of the nuclear spins. Simulations of these NMR spectra in terms of the radial electric fields of either donor-bound electrons or excitons indicate differences, where the bound-exciton model provides a significantly better fit to the data. The same spin physics enabled our measurement of the heterojunction interfacial field, which we find to be less than 1.3 kV/cm at the sites responsible for optical NMR. Other simulations show the promise of optical NMR as a tool in future studies aimed at atomic-level characterization of quantum-confined systems such as quantum dots and wells.
", "doi": "10.7907/0JZB-N948", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:8140", "collection": "thesis", "collection_id": "8140", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03172014-143110747", "primary_object_url": { "basename": "Lobo_jd_2001.pdf", "content": "final", "filesize": 34032403, "license": "other", "mime_type": "application/pdf", "url": "/8140/1/Lobo_jd_2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Experimental Chemical Physics of Droplets and Clusters", "author": [ { "family_name": "Lobo", "given_name": "Julio Danin", "clpid": "Lobo-Julio-Danin" } ], "thesis_advisor": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Time-of-flight measurements of energetic He atoms, field ionization of cryogenic liquid\r\nhelium clusters, and time-of-flight and REMPI spectroscopy of radical salt clusters were\r\ninvestigated experimentally. The excited He atoms were generated in a corona\r\ndischarge. Two strong neutral peaks were observed, accompanied by a prompt photon\r\npeak and a charged peak. All peaks were correlated with the pulsing of the discharge.\r\nThe neutral hyperthermal and metastable atoms were formed by different mechanisms\r\nat different stages of the corona discharge. Positively charged helium droplets were\r\nproduced by ionization of liquid helium in an electrostatic spraying experiment. The fluid\r\nemerging from a thin glass capillary was ionized by a high voltage applied to a needle\r\ninside the capillary. Fine droplets (less than 10 \u00b5m in diameter) were produced in showers with\r\ncurrents as high as 0.4 \u00b5A at 2-4 kV. The high currents resulting from field ionization in\r\nhelium and the low surface tension of He I, led to charge densities that greatly exceeded\r\nthe Rayleigh limit, thus resulting in coulombic explosion of the liquid. In contrast, liquid\r\nnitrogen formed a well-defined Taylor cone with droplets having diameters comparable\r\nto the jet (\u2248100 \u00b5m) at lower currents (10 nA) and higher voltages (8 kV). The metal-halide\r\nclusters of calcium and chlorine were generated by laser ablation of calcium metal\r\nin a Ar/CCl4 expansion. A visible spectrum of the Ca2Cl3 cluster was observed from 651\r\nto 630 nm by 1 +1' REMPI. The spectra were composed of a strong origin band at 15\r\n350.8 cm-1 and several weak vibronic bands. Density functional calculations predicted\r\nthree minimum energy isomers. The spectrum was assigned to the 2B2 \u2190 X 2A1\r\ntransition of a planar C2V structure having a ring of two Cl and two Ca atoms and a\r\nterminal Cl atom. The ring isomer of Ca2Cl3 has the unpaired electron localized on one\r\nCa2+ ion to form a Ca+ chromophore. A second electronic band of Ca2Cl3 was observed at 720 nm. The band is sharply different from the 650 nm band and likely due to a\r\ndifferent isomer.", "doi": "10.7907/84nr-p931", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:14500", "collection": "thesis", "collection_id": "14500", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02162022-191638374", "primary_object_url": { "basename": "On_the_theory_of_electron_tran.pdf", "content": "final", "filesize": 8192248, "license": "other", "mime_type": "application/pdf", "url": "/14500/1/On_the_theory_of_electron_tran.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "On the Theory of Electron Transfer Reactions: Superexchange Coupling and Polar Solvation Dynamics", "author": [ { "family_name": "Hsu", "given_name": "Chao-Ping", "orcid": "0000-0002-7187-427X", "clpid": "Hsu-Chao-Ping" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A recursion relation is formulated for the Green's function for calculating the effective electron coupling in bridge-assisted electron transfer systems, within the framework of the tight-binding Hamiltonian. The non-perturbative recursion expression relates the Green\u2019s function of a chain bridge to that of a bridge which is one unit less. The method is used to calculate the electronic coupling between a gold electrode and each of the molecules. (\u03b7\u2075-C\u2085H\u2085)Fe(\u03b7\u2075-C\u2085H\u2084)CO\u2082(CH\u2082)\u2099SH and (\u03b7\u2075-C\u2085H\u2085)Fe(\u03b7\u2075-C\u2085H\u2084)(CH\u2082)\u2099SH (n = 3 to 50). At larger numbers of bridge units, the effective coupling strength shows an exponential decay as the number of methylene units increases. This sequential formalism shows numerical stability even for a very long chain bridge and. since it uses only small matrices, requires much less computer time for the calculation. Identical bridge units are not a requirement, and so the method can be applied to more complicated systems, such as proteins. Most of the calculated coupling strengths, if converted to rate constants according to a nonadiabatic expression, agree well with the experimental results.
\r\n\r\nThe time-dependent dynamic Stokes shift function, which describes the solvent response to a sudden change in the charge distribution of a solute molecule, is expressed in terms of experimentally measured dielectric dispersion data of the solvent, using a simple dielectric continuum model. The result is applied to photoexcited coumarin 343 in water, and encouraging agreement with the experimental data is obtained. A simple formula is also derived which includes the effect of a pump pulse of finite duration. Such an effect is negligible when the frequency of a pump pulse is close to the maximum in the absorption spectrum, but a deviation from the standard formula can be expected for the pump pulse tuned to a far wing of the absorption band of the chromophore. To calculate further the time-dependent fluorescence spectral lineshapes, a method is described for incorporating the vibronic transitions of a solute molecule. The intramolecular vibrational relaxation is assumed to be much faster\r\nthan the observation delay time. Calculations are made for coumarin 153 in acetonitrile. The results are again in encouraging agreement with experimental spectra. Results are also given for the dynamic Stokes shift in methanol.
", "doi": "10.7907/k5yt-g844", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:17573", "collection": "thesis", "collection_id": "17573", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07302025-155308477", "primary_object_url": { "basename": "Moore_TA_1998.pdf", "content": "final", "filesize": 43761299, "license": "other", "mime_type": "application/pdf", "url": "/17573/1/Moore_TA_1998.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Molecular Beam Studies of Stratospheric Photochemistry", "author": [ { "family_name": "Moore", "given_name": "Teresa Anne", "clpid": "Moore-Teresa-Anne" } ], "thesis_advisor": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Photochemistry of chlorine oxide containing species plays a major role in stratospheric\r\nozone depletion. This thesis discusses two photodissociation studies of the key molecules\r\nClONO2 and ClOOCl which were previously thought to only produce Cl-atom ( ozone\r\ndepleting) products at wavelengths relevant to the stratosphere. The development of a\r\nmolecular beam source of ClOOCl and the photodissociation dynamics of the model system\r\nCl2O are also discussed.
\r\n\r\nIn the first chapter, the photochemistry of ClONO2 is examined at 308 run using the\r\ntechnique of photofragment translational spectroscopy. Two primary decomposition\r\npathways, leading to Cl+ NO3 and ClO + NO2, were observed, with a lower limit of 0.33 for\r\nthe relative yield of ClO. The angular distributions for both channels were anisotropic,\r\nindicating that the dissociation occurs within a rotational period.
\r\n\r\nChapter two revisits the photodissociation dynamics of Cl2O at 248 and 308 nm, on\r\nwhich we had previously reported preliminary findings. At 248 nm, three distinct dissociation\r\npathways leading to Cl + ClO products were resolved. At 308 nm, the angular distribution\r\nwas slightly more isotropic that previously reported, leaving open the possibility that Cl2O\r\nexcited at 308 run lives longer than a rotational period.
\r\n\r\nChapter three describes the development and optimization of a molecular beam source\r\nof ClOOCl. We utilized pulsed laser photolysis of Cl2O to generate ClO radicals, and cooled\r\nthe cell to promote three body recombination to form ClOOCl. The principal components in\r\nthe beam were Cl2, Cl2O, and ClOOCl.
\r\n\r\nIn the fourth chapter, the photodissociation dynamics of ClOOCl are investigated at\r\n248 and 308 nm. We observed multiple dissociation pathways which produced ClO + ClO\r\nand 2Cl + O2 products. The relative Cl:ClO product yields are 1.0:0.13 and 1.0:0.20 for\r\nClOOCl photolysis at 248 and 308 run, respectively. The data at 308 nm was more difficult\r\nto interpret because of extensive interference from Cl2 and Cl2O byproducts. The upper limit\r\nfor the relative yield of the ClO + ClO channel was 0.19 at 248 nm and 0.31 at 308 nm.\r\nThese results substantially confirm the current assumption but decrease somewhat the\r\nefficiency of the ClOOCl ozone-depleting catalytic cycle. At 248 run, ClOOCl photolysis\r\nexhibited novel dissociation dynamics which appeared to depend on the symmetry of the\r\nexcited state.
", "doi": "10.7907/nkqt-qj82", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:14503", "collection": "thesis", "collection_id": "14503", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02172022-233103988", "primary_object_url": { "basename": "New_methods_for_the_study_of_i.pdf", "content": "final", "filesize": 5555990, "license": "other", "mime_type": "application/pdf", "url": "/14503/1/New_methods_for_the_study_of_i.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "New Methods for the Study of Intramolecular and Solvent Dynamics", "author": [ { "family_name": "Mehta", "given_name": "Aseem", "clpid": "Mehta-Aseem" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Some of the fastest processes of relevance to chemical physicists occur on pico to femtosecond timescales. In the following chapters two of such fast processes axe investigated with novel theoretical methods to obtain insight into experimental observations at the molecular level.
\r\n\r\nOne of the major topics of interest in chemical physics has been about energy localization in polyatomic molecules. The \"golden rule\" formula states that the rate for the intramolecular relaxation of energy (IVR) that is initially localized in one part of the molecule is proportional to the density of states at that energy. Here, a general mechanism of the energy redistribution out of an initially populated \"light\" or \"bright\" state is elucidated. It is shown that, for a family of acetylenic molecules, the relaxation is due to a sequence of weak off-resonant directly coupled states rather than all the available states. This mechanism shows how the rates of IVR can be significantly slower than those predicted by a naive application of the \"golden rule,\" since mainly only the initial weak off-resonant couplings govern the rate of IVR.
\r\n\r\nAnother topic that has attracted substantial interest in the chemical physics community is that of solvation. Various heavily applied theories of reaction rates, such as the electron transfer theory, have viewed the solvent as a dielectric continuum. Recent experiments and simulations have shown that the very fast solvation response provides interesting information on the molecular nature of the solvent. Here, a new method for doing molecular dynamics (MD) calculations for solvation is developed. This method uses the reaction field method to obtain the long range potential for a small cluster of molecules rather than using the usual Ewald sum technique with periodic boundary conditions (PBC). It is shown, here, that this method may be used successfully for solvent dynamics simulations. This method may prove superior for such calculations as compared to the PBC approach, since it does not impose an artificial isotropy on the problem as is the case with the PBC calculations.
", "doi": "10.7907/75xn-rr09", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:14502", "collection": "thesis", "collection_id": "14502", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02172022-225929135", "primary_object_url": { "basename": "Quantum_effects_in_electron_tr.pdf", "content": "final", "filesize": 4039615, "license": "other", "mime_type": "application/pdf", "url": "/14502/1/Quantum_effects_in_electron_tr.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Quantum Effects in Electron Transfer Reactions and Solvation Dynamics", "author": [ { "family_name": "Song", "given_name": "Xueyu", "orcid": "0000-0001-5142-4223", "clpid": "Song-Xueyu" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis focuses on the quantum effects of electron transfer reactions in solutions and solvation dynamics of pure solvent. A prototypical model system, the\r\nFe\u207a\u00b2 + Fe\u207a\u00b3 \u21cc Fe\u207a\u00b3 + Fe\u207a\u00b2 reaction in water, is treated using the spin-boson Hamiltonian model. The spectral density is related to the experimentally accessible data\r\non the dielectric dispersion of the solvent, using a dielectric continuum approximation. On this basis the quantum correction for the ferrous-ferric electron transfer rate is found to be a factor of 9.6, which is significantly smaller than the corresponding values calculated from molecular models which neglect the electronic and vibrational polarization of the solvent. Using an imaginary free energy method, a general formula for the rate valid in all orders of perturbation in electronic coupling is derived for a renormalized classical bath. It is found that the quantum degrees of freedom can be effectively eliminated from the model by renormalizing the electronic coupling matrix element to the first order approximation for the quantum modes. Furthermore, a similar result is obtained for the quantum bath with a better approximation scheme. In application it has been shown that the rate has a nonmonotonic behavior as a function of the coupling matrix element in the inverted region. In the solvent dynamics controlled regime a one-particle Green function method is used to calculate the electron transfer reaction rate with a spin-boson Hamiltonian. A quantum version of Zusman\u2019s result on solvent dynamical effect in electron transfer reactions is obtained for the symmetric case. It is shown that the quantum effect for most of the realistic systems is not significant at room temperature and it would become important for some fast dielectric relaxation solvents like water. In solvation dynamics studies a Gaussian field model is used to obtain the charge density correlation function of the solution in terms of charge density correlation function of the solvent. It then becomes possible to calculate the time-dependent solvation free energy without using the \"uniform dielectric approximation.\" It is found that the nonuniformity in the vicinity of the solute indeed retards the solvation relaxation.", "doi": "10.7907/ejw2-cy95", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:11174", "collection": "thesis", "collection_id": "11174", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09062018-160235948", "primary_object_url": { "basename": "Stroud_CK_1994.pdf", "content": "final", "filesize": 41667015, "license": "other", "mime_type": "application/pdf", "url": "/11174/1/Stroud_CK_1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Collinear Reaction Dynamics and Hydrodynamic Analysis of the Vibrationally Excited Cl + HCl \u2192 ClH + Cl, Cl + DCl \u2192 ClD + Cl and Cl + TCl \u2192 ClT + Cl Reactions on Two Leps Surfaces", "author": [ { "family_name": "Stroud", "given_name": "Carrie Kim", "clpid": "Stroud-Carrie-Kim" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Quantum dynamical calculations for the collinear Cl + HCl \u2192 ClH + Cl, Cl + DCl \u2192 ClD + Cl, and Cl + TCl \u2192 ClT + Cl reactions on low and high barrier potential energy surfaces are presented and discussed within the framework of the hyperspherical coordinate representation. Vibrational excitation of the reagent diatomic is found to decrease the reaction rate for the low barrier surface and increase the reaction rate for the high barrier surface. Quantum mechanical streamline calculations and tunneling fractions are used for analysis, and discussion of the results is made in terms of the topology of the potential surface, in which the skew angle and barrier height of the system play a leading role in explaining the dynamics of the reaction.
", "doi": "10.7907/aqts-fq51", "publication_date": "1994", "thesis_type": "masters", "thesis_year": "1994" }, { "id": "thesis:7395", "collection": "thesis", "collection_id": "7395", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01112013-110414331", "type": "thesis", "title": "Atomic-Scale Imaging and Spectroscopy Using Scanning Tunneling Microscopy", "author": [ { "family_name": "Youngquist", "given_name": "Michael George", "clpid": "Youngquist-Michael-George" } ], "thesis_advisor": [ { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" }, { "family_name": "Kaiser", "given_name": "William J.", "clpid": "Kaiser-William-J" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Advances in scanning tunneling microscopy (STM) instrumentation\r\nand applications are presented. An ultrahigh vacuum (UHV) scanning\r\ntunneling microscope incorporating computer-controlled two-dimensional\r\nsample translation and in vacuo tip and sample transfer was developed. Its\r\nperformance is documented through large-area and atomic-resolution\r\nimaging of highly stepped Si(111) 7x7 reconstructed surfaces and physisorbed\r\nclusters on graphite. An STM with automated approach and intra-Dew\u00e4r\r\nspring suspension was developed for operation in cryogenic liquids. A high\r\nperformance digital signal processor (DSP) based control system was\r\nconstructed, and software with advanced spectroscopic imaging and data\r\nprocessing capabilities was developed.
\r\n\r\nThe feasibility of individual-molecule vibrational spectroscopy via\r\nSTM-detected inelastic electron tunneling is assessed. In preliminary\r\nexperiments, a low-temperature STM was used for energy gap and phonon\r\nspectroscopy of superconducting Pb films. The first STM observation of\r\nphonon density of states effects in a superconductor is reported.
\r\n\r\nA systematic UHV STM imaging and spectroscopy study of 2H-MoS_2\r\nwas conducted. Atom-resolved images from three distinct imaging modes\r\nare presented. Occasional appearance of negative differential resistance\r\n(NOR) in I vs. V measurements is traced to changing tip electronic structure\r\nrather than localized surface states. Other potential NOR mechanisms are\r\ndiscussed including electron trap charging and resonant tunneling through a\r\ndouble-barrier quantum well structure arising from layer separation in the\r\nMoS_2 crystal.
\r\n\r\nDNA was imaged at atomic resolution with a UHV STM. Images show\r\ndouble-helical structure, base pairs, and atomic-scale substructure.\r\nExperimental STM profiles have atom-for-atom correlation with the A-DNA\r\nvan der Waals surface. This work demonstrates the potential of the STM for\r\ncharacterization of large biomolecular structures.
\r\n\r\nImpurity-pinned steps on silicon and gold surfaces were imaged by\r\nSTM. Pinned gold steps have short linear coherence lengths and form step\r\nloops at impurities by an Orowan-type bypassing mechanism. Step loops\r\nwere not observed at Si(111) pinning sites; step contours seem to be correlated\r\nwith the degree of order in the Si surface reconstruction.
", "doi": "10.7907/0d6k-be86", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:8005", "collection": "thesis", "collection_id": "8005", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10232013-093350784", "type": "thesis", "title": "Electron Energy-Loss Spectroscopy Study of Polyatomic Molecular Systems Under Pyrolytic Conditions", "author": [ { "family_name": "Xavier", "given_name": "Isaac de Melo, Jr.", "clpid": "Xavier-Isaac-de-Melo-Jr" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Weitekamp", "given_name": "Daniel P.", "orcid": "0000-0003-0079-8000", "clpid": "Weitekamp-D-P" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "orcid": "0000-0001-6547-1469", "clpid": "Marcus-R-A" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The technique of variable-angle, electron energy-loss spectroscopy has been used to study the electronic spectroscopy of the diketene molecule. The experiment was performed using incident electron beam energies of 25 eV and 50 eV, and at scattering angles between 10\u00b0 and 90\u00b0. The energy-loss region from 2 eV to 11 eV was examined. One spin-forbidden transition has been observed at 4.36 eV and three others that are spin-allowed have been located at 5.89 eV, 6.88 eV and 7.84 eV. Based on the intensity variation of these transitions with impact energy and scattering angle, and through analogy with simpler molecules, the first three transitions are tentatively assigned to an n \u2192 \u03c0* transition, a \u03c0 - \u03c3* (3s) Rydberg transition and a \u03c0 \u2192 \u03c0* transition.
\r\n\r\nThermal decomposition of chlorodifluoromethane, chloroform, dichloromethane and chloromethane under flash-vacuum pyrolysis conditions (900-1100\u00b0C) was investigated by the technique of electron energy-loss spectroscopy, using the impact energy of 50 eV and a scattering angle of 10\u00b0. The pyrolytic reaction follows a hydrogen-chloride \u03b1-elimination pathway. The difluoromethylene radical was produced from chlorodifluoromethane pyrolysis at 900\u00b0C and identified by its X̃\u00b9A\u2081 \u2192 Ã\u00b9B\u2081 band at 5.04 eV.
\r\n\r\nFinally, a number of exploratory studies have been performed. The thermal decomposition of diketene was studied under flash vacuum pressures (1-10 mTorr) and temperatures ranging from 500\u00b0C to 1000\u00b0C. The complete decomposition of the diketene molecule into two ketene molecules was achieved at 900\u00b0C. The pyrolysis of trifluoromethyl iodide molecule at 1000\u00b0C produced an electron energy-loss spectrum with several iodine-atom, sharp peaks and only a small shoulder at 8.37 eV as a possible trifluoromethyl radical feature. The electron energy-loss spectrum of trichlorobromomethane at 900\u00b0C mainly showed features from bromine atom, chlorine molecule and tetrachloroethylene. Hexachloroacetone decomposed partially at 900\u00b0C, but showed well-defined features from chlorine, carbon monoxide and tetrachloroethylene molecules. Bromodichloromethane molecule was investigated at 1000\u00b0C and produced a congested, electron energy-loss spectrum with bromine-atom, hydrogen-bromide, hydrogen-chloride and tetrachloroethylene features.
", "doi": "10.7907/4wx9-6j66", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:554", "collection": "thesis", "collection_id": "554", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-130036", "type": "thesis", "title": "Experimental Probes of Gas Phase Ions and Molecules: I. Product Kinetic Energy Release Measurements as a Probe of Reaction Thermochemistry, Dynamics, and Chemical Structure in Systems Containing Transition Metal Ions. II. Photoelectron and Optical Studies of Organic Transient Species", "author": [ { "family_name": "Dearden", "given_name": "David Vernell", "clpid": "Dearden-David-Vernell" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The release of kinetic energy in the decomposition of a metastable ion is a reflection of both the overall energetics and the potential energy surface on which the process takes place. Chapter 1 applies measurements of the kinetic energy release distributions (KERDs) for decomposition of metastable Mn(CO)\u2093\u207a to the dynamics and energetics of exchange processes for the CO ligands. All the dissociations can be described by statistical phase space theory, in agreement with efficient CO exchange rates indicating that conservation of electronic spin is not important to the dynamics. A general method is presented and used whereby Mn\u207a-CO bond energies are obtained from the KERDs. Chapter 2 deals with reactions of Fe\u207a and Co\u207a with alkanes to eliminate methane, which have KERDs narrower than predicted by statistical theory. Restriction of the angular momentum (or, equivalently, the impact parameter) to values less than those anticipated by simple ion-molecule collision theory can account for the narrowed distributions. The restrictions result from barriers in the effective potential energy surfaces and from limitations in our measurement techniques. In Chapter 3, KERDs are used to demonstrate the existence of cobaltacyclobutane\u207a, (hydrido)(cyclopropyl)Co\u207a and Co(propene)\u207a structures which do not interconvert on the \u00b5s time scale in the gas phase. Chapter 4 deals with the dehydrogenations of cyclic alkanes by Fe\u207a and Co\u207a, and shows that, contrary to previous assumptions, statistical energy partitioning occurs in these processes.
\r\n\r\nChapters 5 and 6 deal with studies of transient organic species. Chapter 5 presents preliminary work on charge-reversed, resonance enhanced multiphoton ionization (CRREMPI), a potentially powerful new method which exploits the special characteristics of the ion cyclotron resonance spectrometer to obtain optical spectra of a wide variety of transient species. In Chapter 6 photoelectron spectroscopy is used to observe the rearrangements of primary alkyl radicals, produced by flash vacuum pyrolysis of nitrites, to the thermodynamically more stable secondary isomers. Decomposition processes are also observed.
", "doi": "10.7907/6tyj-gy42", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:7510", "collection": "thesis", "collection_id": "7510", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03122013-093032947", "primary_object_url": { "basename": "Parker_gr_1988.pdf", "content": "final", "filesize": 97733769, "license": "other", "mime_type": "application/pdf", "url": "/7510/1/Parker_gr_1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Determination of Nascent H\u2082 Rovibrational Distributions by Laser Induced Fluorescence: Applications to Formaldehyde Photodissociation and Hydrogen Exchange Reactions", "author": [ { "family_name": "Parker", "given_name": "Garth Rockwood, Jr.", "clpid": "Parker-Garth-Rockwood-Jr" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Individual quantum states of H\u2082 have been detected using the technique of Laser Induced Fluorescence. This technique is extremely sensitive, with a detection sensitivity of 6 x 10\u2078 states cm\u207b\u00b3 in a probed volume of 0.029 cm\u00b3 with a signal-to-noise ratio of 3. This technique is also accurate. A spectrum of room temperature H\u2082 had a rotational temperature of 305.8 \u00b1 3.0 K. LIF detection of H\u2082 was used to study the H\u2082CO photodissociation reaction under essentially collision-free conditions. Following excitation of the rR\u2083 bandhead of the 2\u00b9\u20804\u00b3\u2080 transition at 30388.5 cm\u207b\u00b9, the principal product was ortho-H\u2082. States as high as v = 4, J = 5 were seen. Within the v = 1 channel, the rotational distribution peaked at J = 3. Following excitation of the rR\u2084 bandhead of the 2\u00b9\u20804\u00b3\u2080 transition at 30396.7 cm\u207b\u00b9, the principal product was para-H\u2082. This is the first report of the para-H\u2082 distribution following H\u2082CO dissociation. The rotational distribution is similar to that for ortho-H\u2082 and peaks at J = 4 within v = 1 channel. This result contradicts a recent theoretical calculation that predicted that the para-H\u2082 distribution would be bimodal with a minimum at J = 6. Quantitative analysis of higher vibrational levels was hampered by a lack of spectroscopic knowledge (both transition energies and intensities) when the the B̅ and C̅ states perturb each other. Attempts to use LIF to study the hydrogen exchange reaction have been unsuccessful.
", "doi": "10.7907/ht1t-df04", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7411", "collection": "thesis", "collection_id": "7411", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01182013-144750308", "primary_object_url": { "basename": "Dubs_rl_1988.pdf", "content": "final", "filesize": 20048491, "license": "other", "mime_type": "application/pdf", "url": "/7411/1/Dubs_rl_1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Single- and Multiphoton Ionization Processes in Molecules", "author": [ { "family_name": "Dubs", "given_name": "Richard Leslie", "clpid": "Dubs-Richard-Leslie" } ], "thesis_advisor": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "clpid": "Dougherty-D-A" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "clpid": "Weitekamp-D-P" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation is theoretical in nature and can be separated into two main areas: 1) single- and multiphoton ionization studies of a novel photoelectron effect, and 2) single-photon ionization studies of simple clusters as models for adsorbate photoemission. The first area centers on the phenomenon of circular dichroism in photoelectron angular distributions (CDAD). CDAD is shown to exist from oriented linear molecules, adsorbed atoms, and aligned atoms and molecules in the gas phase. The calculations presented here are the first to demonstrate the experimental feasability of CDAD studies. CDAD is shown to be a measurable effect which exists because the photoelectron collection direction can break the symmetry of these otherwise highly symmetric systems. As a direct result of the work presented here, CDAD has now been observed experimentally. Coupled with resonantly enhanced multiphoton ionization (REMPI), CDAD is shown to be a powerful probe of unknown alignment in gas phase atomic and molecular samples. The second area of research focuses on the simple oriented molecules NiCO and NiN\u2082 as models for the corresponding adsorbate systems. These simple models provide insight into features observed in the experimental angle-resolved photoemission spectra.
", "doi": "10.7907/63a3-d438", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7412", "collection": "thesis", "collection_id": "7412", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01182013-155753371", "primary_object_url": { "basename": "Cline III_ji_1988.pdf", "content": "final", "filesize": 27990114, "license": "other", "mime_type": "application/pdf", "url": "/7412/1/Cline III_ji_1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Photodissociation Dynamics of Triatomic van der Waals Molecules", "author": [ { "family_name": "Cline", "given_name": "Joseph Isaac, III", "clpid": "Cline-Joseph-Isaac-III" } ], "thesis_advisor": [ { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The spectroscopy and vibrational predissociation dynamics of triatomic van der Waals molecules are studied experimentally and theoretically at the state-to-state level of detail.
\r\n\r\nLaser-induced fluorescence spectra of HeCl2 are measured and the geometry and vibrational predissociation rate are obtained by a rotational analysis of the spectra and the determination of homogenous linewidths. A laser pump-probe technique is used to measure the vibrational and rotational state population distribution of the product Cl2. Although the Cl2 fragment has little rotational energy, its rotational distribution is bimodal. A symmetry selection rule for the dissociation results from the symmetry of the He \u2022 \u2022 \u2022 Cl2 van der Waals potential. Quantum mechanical calculations on a realistic potential energy surface are successful in modeling the experimental spectroscopy and dynamics.
\r\n\r\nThe vibrational predissociation dynamics of NeCl2 is also measured using the pump-probe technique. In this case the Cl2 fragment shows significantly more rotational excitation than in the dissociation of HeCl2. The rotational distributions are bimodal and are relatively independent of the energy of the prepared state. The NeCl2 binding energy is estimated from thresholds for the populations of fragment rotational levels.
\r\n\r\nThe vibrational predissociation of NeBr2 is studied by dispersing the fluorescence of the Br2 fragment. The product Br2 is rotationally cold. The closure of vibrational product channels is used to determine the binding energy of the molecule.
", "doi": "10.7907/f38f-hb60", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7413", "collection": "thesis", "collection_id": "7413", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01182013-160624319", "primary_object_url": { "basename": "Hair_sr_1988.pdf", "content": "final", "filesize": 22905638, "license": "other", "mime_type": "application/pdf", "url": "/7413/1/Hair_sr_1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Experimental and Theoretical Studies of van der Waals Molecule Photodissociation", "author": [ { "family_name": "Hair", "given_name": "Sally Reid", "clpid": "Hair-Sally-Reid" } ], "thesis_advisor": [ { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Three studies are reported on the vibrational predissociation of polyatomic van der Waals complexes. In the first, the ethylene dimer and rare gas-ethylene complexes are treated theoretically, using a local mode quantum mechanical technique. The ethylene dimer exhibits extensive mixing between the initially excited \u03bd\u2087 vibration and nearby combinations of the \u03bd\u2081\u2080 and van der Waals vibrations, while the rare gas- ethylene complexes do not. Mixing is extensive enough in the ethylene dimer to spread the oscillator strength of the \u03bd\u2087 vibration over a 10 cm\u207b\u00b9 region of the spectrum, in agreement with the experimentally observed band.
\r\n\r\nThe second study is a low resolution photodissociation experiment on the ethylene-methane complex. The spectra observed by exciting the \u03bd\u2087 ethylene vibration of C\u2082H\u2084-CH\u2084, C\u2082H\u2084-CH\u2082D\u2082, and C\u2082H\u2084-CD\u2084 all exhibit the same width. This indicates that the shapes and widths of the observed spectra are not determined by unresolved or power-broadened rotational structure. This result underscores the importance of vibrational coupling in the dissociation process.
\r\n\r\nThe final study is a laser pump-probe experiment on the Ne\u2082Cl\u2082 and Ne\u2083Cl\u2082 complexes. The Ne\u2082Cl\u2082 complex has a distorted tetrahedral geometry, as determined from high resolution, excitation spectra. Excitation shift arguments suggest a structure for Ne\u2083Cl\u2082 with the three neon atoms encircling the Cl\u2082 bond axis. The total van der Waals bond energy of the Ne\u2082Cl\u2082 complex is found to be between 145.6 and 148.6 cm\u207b\u00b9. When energetically possible, the Ne\u2082Cl\u2082 complex can dissociate by losing a single quantum of Cl\u2082 stretching energy. This indicates that the two neon atoms do not dissociate by two independent \"half-collisions.\" The Cl\u2082 fragment rotational excitation is found to depend only weakly on the energy available to the fragments.
\r\n\r\n\r\n", "doi": "10.7907/anb1-sr68", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7419", "collection": "thesis", "collection_id": "7419", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01222013-110555654", "type": "thesis", "title": "Three Dimensional Atom-Diatom Reactive Scattering Calculations Using Symmetrized Hyperspherical Coordinates", "author": [ { "family_name": "Hipes", "given_name": "Paul Gregory", "clpid": "Hipes-Paul-Gregory" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Dervan", "given_name": "Peter B.", "clpid": "Dervan-P-B" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The focus of this thesis is the use of symmetrized hyperspherical coordinate techniques in the accurate calculation of differential cross sections for the reactive collision of an atom with a diatomic molecule in three-dimensional space. A single set of symmetrized hyperspherical coordinates treats all regions of configuration space in an equivalent inelastic scattering problem which is conceptually and computationally easier to handle.
\r\n\r\nThe work described here represents the first successful application of any accurate hyperspherical coordinate methodology to atom-diatom reactive scattering in three-dimensional space. This methodology has permitted the calculation of zero total angular momentum (J = 0) partial wave transition probabilities and associated phases over a significantly larger range of collision energies (up to 1.6 eV total energy) than previously possible for the system H + H\u2082. The numerical stability of the treatment is sufficiently high to permit the first lifetime matrix analysis of the resonance structure of H + H\u2082 based on scattering matrices from our accurate calculations. This analysis reveals a series of 6 resonance states in the J = 0 partial wave, some of which have not been seen before. The symmetrized hyperspherical coordinate methodology is presented in detail. A selection of surface functions and scattering results for J = 0 H + H\u2082 using the LSTH potential energy surface are presented and discussed. In addition, a small number of results from the Porter-Karplus potential energy surface are also given.
\r\n", "doi": "10.7907/2S8G-PJ87", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7501", "collection": "thesis", "collection_id": "7501", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03062013-161416978", "primary_object_url": { "basename": "Klippenstein 1988.pdf", "content": "final", "filesize": 37105558, "license": "other", "mime_type": "application/pdf", "url": "/7501/1/Klippenstein 1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Theoretical Studies of Chemical Reaction Dynamics", "author": [ { "family_name": "Klippenstein", "given_name": "Stephen Jacob", "clpid": "Klippenstein-Stephen-Jacob" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "clpid": "Dougherty-D-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In this thesis theoretical models a.re developed and/or applied to the study of the dynamics of a variety of chemical reactions. First, a semiclassical model is developed to describe the effect of mutual orientation of the donor and acceptor on the rate of electron transfer between two large aromatic groups. The next reaction considered is that of gas phase H-atom transfer reactions. In this case a comparison is made of two previously developed approximations for the treatment of the particular case of H-atom transfer between two heavy particles.
\r\n\r\nThe next topic involves the study of the rate of intramolecular vibrational redistribution of energy. First, an iterative procedure is developed for determining more and more accurate effective Hamiltonians for the description of the dynamics. The foundation of this method is the separation of the basis states into resonant and nonresonant sets followed by an adiabatic approximation for the dynamics of the off-resonant set. A second study involves the application of artificial intelligence techniques to the choice of a small set of basis states which are the states of greatest importance to the redistribution dynamics.
\r\n\r\nThe remainder of the thesis is devoted to the study of those unimolecular dissociation/free radical recombination reactions which contain highly flexible transition states. For these reactions, a method for determining the quantum partition function for the transition state in terms of path integral ratios is developed and applied to the study of the thermally activated methyl radical recombination. Subsequently, a method is developed for determining the number of states, for the transition state, at a given energy and angular momentum. The basis of the method is the use of conventional Euler angle coordinates in the Monte Carlo evaluation of phase space integrals. This method is applied to the NCNO, CH\u2082CO, and H\u2082O\u2082 photodissociation processes. Also presented is a discussion of both the trend of the location of the transition state with increasing energy and the possible influence of excited potential energy surfaces.
\r\n", "doi": "10.7907/dbrd-wj15", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7505", "collection": "thesis", "collection_id": "7505", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03082013-103249804", "primary_object_url": { "basename": "Lederman 1988.pdf", "content": "final", "filesize": 13779316, "license": "other", "mime_type": "application/pdf", "url": "/7505/1/Lederman 1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Artificial Intelligence in Quantum Intramolecular Dynamics with Application to a Heavy Central Mass Problem", "author": [ { "family_name": "Lederman", "given_name": "Steven Mark", "clpid": "Lederman-Steven-Mark" } ], "thesis_advisor": [ { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" } ], "thesis_committee": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation consists in effect, of three parts, each involving some aspect of intramolecular vibrational relaxation. The first section contains simple approximate statistical formulas for the density of vibrational and rovibrational states by symmetry type for non-linear molecules. A modified Whitten-Rabinovitch estimate of the density of states by symmetry type for linear molecules is also derived. Sample calculations are given, which serve to demonstrate the accuracy of all formulas given. In the second section, a 4-coordinate model is presented and is used to treat the vibrational energy redistribution in a molecule with a heavy central metal atom. Local group modes are identified using perturbation theory, and their dynamical separation and importance in analyzing energy redistribution is noted. A comparison of classical and quantum calculations on the model system is also given. In the third section, artificial intelligence methods are used to treat the time-evolution of intramolecular quantum dynamics. Comparison is made of several AI search algorithms and of evaluation functions, proposed here, in an application to the study of quantum intramolecular vibrational relaxation. The methods developed are applied to an 11-coordinate heavy central mass problem and are used to treat both vibrational quantum beats and \"dissipative\" intramolecular energy transfer.
", "doi": "10.7907/8333-3M02", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:11871", "collection": "thesis", "collection_id": "11871", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10292019-111940086", "primary_object_url": { "basename": "Walzl_KN_1987.pdf", "content": "final", "filesize": 35005109, "license": "other", "mime_type": "application/pdf", "url": "/11871/1/Walzl_KN_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Variable-Angle Electron Energy-Loss Spectroscopy of Polyatomic Molecular Systems", "author": [ { "family_name": "Walzl", "given_name": "Kerry Neil", "clpid": "Walzl-Kerry-Neil" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Zewail", "given_name": "Ahmed H.", "clpid": "Zewail-A-H" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Dervan", "given_name": "Peter B.", "clpid": "Dervan-P-B" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The technique of variable-angle electron energy-loss spectroscopy has been used to study the electronic spectroscopy and structure of both open- and closed-shell molecules. The experiments were performed using incident electron beam energies between 25 eV and 100 eV and at scattering angles between 0\u00b0 and 90\u00b0. Energy-loss regions from 0 eV to 16 eV were examined. Spin-forbidden, dipole symmetry-forbidden/quadrupole symmetry-allowed, and super-excited transitions were investigated by this method.
\r\n\r\nThe three small carbonyl compounds formaldehyde (CH2O), acetaldehyde (C2H4O), and acetone (C3H6O) were studied in the energy-loss region from 0 eV to 16 eV. Low-lying spin-forbidden n \u2192 \u03c0* and \u03c0 \u2192 \u03c0* transitions were located on the basis of the angular behavior of their relative differential cross sections. High-lying (autoionizing in the case of formaldehyde) dipole symmetry-forbidden states were also assigned on the basis of differential cross section behavior. The effect of methyl substitution on the transition energies was also noted and discussed.
\r\n\r\nFive dicarbonyl compounds (biacetyl, acetylacetone, acetonylacetone, 1,2-cyclohexanedione, 1,4-cyclohexanedione) were investigated by this spectroscopic method in order to locate their low-lying spin-forbidden transitions. The energy difference between the lowest spin-allowed and spin-forbidden n \u2192 \u03c0* excitations in the cyclic dicarbonyls was found to be much larger than in the acyclic dicarbonyls; this difference was discussed.
\r\n\r\nThe spectrum of the methyl radical CH3 was investigated by the same technique as the carbonyls except that the radical was generated by pyrolysis. Three source compounds were tried (tetramethyl tin, ethyl nitrite, di-t-butylperoxide) with temperatures ranging from ambient to 800\u00b0C. Using di-t-butylperoxide at a pyrolysis temperature of about 300\u00b0C, relative differential cross sections for the lowest allowed 2A'1 \u2190 2A\"2 3s Rydberg transition (5.73 eV) were determined at incident energies of 50 eV and 25 eV. The differential cross sections for this band do not indicate the presence of any underlying spin-forbidden transition.
\r\n\r\nFinally, preliminary investigations of the spectroscopy of pyridazine and cyclohexanone were undertaken. For pyridazine, a new low-lying spin-forbidden excitation was observed. The low-lying spin-forbidden transitions of cyclohexanone were also observed along with tentative relative differential cross sections at 30 eV and 50 eV. Rydberg bands in this molecule converging to the first ionization potential were seen and the positions tabulated.
\r\n", "doi": "10.7907/pzpj-5b50", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:8072", "collection": "thesis", "collection_id": "8072", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02122014-142619432", "type": "thesis", "title": "Studies of Molecular Bonding, Interactions and Decomposition Reactions on the (001) Surface of Ruthenium", "author": [ { "family_name": "Toby", "given_name": "Brian H.", "clpid": "Toby-Brian-H" } ], "thesis_advisor": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "thesis_committee": [ { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Marsh", "given_name": "Richard Edward", "clpid": "Marsh-R-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The interactions of N2, formic acid and acetone on the Ru(001) surface are studied using thermal desorption mass spectrometry (TDMS), electron energy loss spectroscopy (EELS), and computer modeling.
\r\n\r\nLow energy electron diffraction (LEED), EELS and TDMS were used to study chemisorption of N2 on Ru(001). Adsorption at 75 K produces two desorption states. Adsorption at 95 K fills only the higher energy desorption state and produces a (\u221a3 x \u221a3)R30\u00b0 LEED pattern. EEL spectra indicate both desorption states are populated by N2 molecules bonded \"on-top\" of Ru atoms.
\r\n\r\nMonte Carlo simulation results are presented on Ru(001) using a kinetic lattice gas model with precursor mediated adsorption, desorption and migration. The model gives good agreement with experimental data. The island growth rate was computed using the same model and is well fit by R(t)m - R(t0)m = At, with m approximately 8. The island size was determined from the width of the superlattice diffraction feature.
\r\n\r\nThe techniques, algorithms and computer programs used for simulations are documented. Coordinate schemes for indexing sites on a 2-D hexagonal lattice, programs for simulation of adsorption and desorption, techniques for analysis of ordering, and computer graphics routines are discussed.
\r\n\r\nThe adsorption of formic acid on Ru(001) has been studied by EELS and TDMS. Large exposures produce a molecular multilayer species. A monodentate formate, bidentate formate, and a hydroxyl species are stable intermediates in formic acid decomposition. The monodentate formate species is converted to the bidentate species by heating. Formic acid decomposition products are CO2, CO, H2, H2O and oxygen adatoms. The ratio of desorbed CO with respect to CO2 increases both with slower heating rates and with lower coverages.
\r\n\r\nThe existence of two different forms of adsorbed acetone, side-on, bonded through the oxygen and acyl carbon, and end-on, bonded through the oxygen, have been verified by EELS. On Pt(111), only the end-on species is observed. On dean Ru(001) and p(2 x 2)O precovered Ru(001), both forms coexist. The side-on species is dominant on clean Ru(001), while O stabilizes the end-on form. The end-on form desorbs molecularly. Bonding geometry stability is explained by surface Lewis acidity and by comparison to organometallic coordination complexes.
\r\n\r\n\r\n\r\n", "doi": "10.7907/R50B-J328", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:11889", "collection": "thesis", "collection_id": "11889", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11042019-153133005", "primary_object_url": { "basename": "celii-fg-1986.pdf", "content": "final", "filesize": 8223625, "license": "other", "mime_type": "application/pdf", "url": "/11889/1/celii-fg-1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. IR Photodissociation Spectroscopy of Large van der Waals Clusters. II. UV Laser-Induced Photochemistry of Fe(CO)\u2085 on Single Crystal Surfaces", "author": [ { "family_name": "Celii", "given_name": "Francis Gabriel", "clpid": "Celii-Francis-Gabriel" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Richards", "given_name": "John H.", "clpid": "Richards-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chapter 2 is a summary of vibrational predissociation spectra of weakly bound clusters containing either CF3I or CF3Br. Spectra indicative of ArCF3I, KrCF3I, (CF3I)2, ArCF3Br and (CF3Br)2 clusters are presented with comparison to the matrix-isolation spectra of CF3I and CF3Br.
\r\n\r\nThe infrared photodissociation technique can be applied to the study of weakly bonded clusters which do not absorb in the infrared by attaching an IR chromophore; this work is presented in Chapter 3. Vibrational predissociation spectra of large clusters of Ar, Kr, N2 and CH4 containing a single CH3F or C2H4 chromophore are obtained as a function of cluster size. The IR spectra distinguish three regimes of cluster size in the CH3F case. The dissociation profiles yield information on the chromophore environment and the lifetime of the excited vibration. The clusters are gas-phase analogies to the matrix-isolation technique, although differences between the two are consistent with the presumed icosahedral cluster geometry, and \"matrix\" and \"surface\" sites are distinguishable.
\r\n\r\nChapter 4 presents the application of a simple two-level-with-decay model to the photodesorption of weakly bound adsorbates on crystal surfaces. Feasibility estimates are reported and establish that vibrational predissociation of the excited adsorbes can be induced in the infrared, where energy quenching mechanisms on surfaces can be quite fast. The effect of these quenching mechanisms on the lineshapes present the opportunity to probe the processes with the use of the photodesorption technique. Extraction of the phenomenological rate constants is described. Also reported are attempts to observe photodesorption induced by low-power lasers.
\r\n\r\nThe photodecomposition of Fe(CO)5 on three single crystal surfaces, sapphire (Al2O3), Si(100) and Ag(110), using UV irradiation is described in Chapter 5. The quenching of excited electronic states of adsorbates is expected to be quite different on the surfaces, yet dissociation of the Fe(CO)5 is observed in all cases. The results allow determination of the dissociation mechanism and also imply that the Fe(CO)5 dissociation rate is ultra-fast (< 10-13). Extensions of this initial investigation are discussed.
", "doi": "10.7907/nz14-wz74", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:11823", "collection": "thesis", "collection_id": "11823", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172019-161305619", "type": "thesis", "title": "Calculation of e\u207b-H Atom Scattering Processes Using Hyperspherical Coordinates", "author": [ { "family_name": "Hood", "given_name": "Diane Marie", "clpid": "Hood-Diane-Marie" } ], "thesis_advisor": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" } ], "thesis_committee": [ { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A method is presented for accurately solving the Schr\u00f6dinger equation for the scattering of an electron from a hydrogen atom in three dimensions, which uses hyperspherical coordinates. Our motivation for using this new technique is that previous methods -- coupled channel expansions using target atom eigenfunctions,1 polarization functions and pseudostates,2 and variational methods3 -- have all proven unsatisfactory. The coupled channel calculations tend to have difficulty obtaining convergence with respect to basis set size, and the variational method interjects spurious resonances. Previous applications of hyperspherical coordinates4 have used methods that, while adequate for computing the energy level of the bound state of H-, are not appropriate to full scattering calculations.
\r\n\r\nWe have obtained converged surface functions at a set of discrete values of the hyperradius, which acts as a parameter. The surface functions are further expanded in a basis set that involves 1-dimensional functions of the hyperspherical angle, which are obtained by a finite difference method.
\r\n\r\nThe surface functions have been used to expand the scattering functions. The resulting coupled equations are solved numerically. The wavefunctions are obtained separately at each energy and are converged with respect to the number of basis functions used. Calculations performed so far give converged results for J = 0 through J = 5 up to the n = 4 threshold. The method is both accurate and efficient, and has been implemented on a VAX 11/780 with an FPS164 attached processor.
\r\n\r\nBoth the magnitude and phase of elements of the scattering matrix have converged. Integral cross sections have been obtained for energies up to the n = 4 threshold of hydrogen. Feshbach resonances have been detected below each threshold, and they have been characterized and classified.
\r\n\r\n1P. G. Burke, S. Ormonde, and W. Whitaker, Proc. Phys. Soc. 92, 319, (1967).
\r\n2S. Geltman and P. G. Burke, J. Phys. B 3, 1062, (1970).
\r\n3J. Callaway, Phys. Rev. A 26, 199, (1982).
\r\n4C. D. Lin, Phys. Rev. A 23, 1585, (1981).
\r\n\r\n", "doi": "10.7907/xj5h-me61", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:11475", "collection": "thesis", "collection_id": "11475", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04162019-162014129", "type": "thesis", "title": "The Determination of Atom-Molecule Interaction Potentials from Total Differential Cross Sections", "author": [ { "family_name": "O'Loughlin", "given_name": "Michael John", "clpid": "O'Loughlin-Michael-John" } ], "thesis_advisor": [ { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A newly constructed crossed molecular beams apparatus has been used to measure total (elastic plus inelastic) differential cross sections for collisions between rare gas atoms and methane and chlorine molecules. The total differential cross sections were then used in an iterative trial and error potential fitting program to determine the interaction potentials between these species. In the rare gas-methane study (Chapter 2), the methane molecule has been approximated as being a spherical entity, and the standard equations and techniques have been applied to simulate the laboratory scattering distributions from an assumed isotropic potential. The isotropic potentials determined in this manner are compared with some recently proposed anisotropic potentials for these systems. In the rare gas-chlorine study (Chapter 3), anisotropic potentials have been determined using the infinite order sudden approximation and a Legendre parameter expansion of a central field potential. The resulting potentials compare rather favorably with what is known about these potential surfaces from photodissociation experiments.
", "doi": "10.7907/eg4t-an16", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:11851", "collection": "thesis", "collection_id": "11851", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10232019-145508172", "type": "thesis", "title": "Elastic, Inelastic, and Photofragment Scattering from Crossed Molecular Beams", "author": [ { "family_name": "Reid", "given_name": "Brian Paul", "clpid": "Reid-Brian-Paul" } ], "thesis_advisor": [ { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Weitekamp", "given_name": "Daniel P.", "orcid": "0000-0003-0079-8000", "clpid": "Weitekamp-D-P" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Three sets of crossed molecular beam scattering experiments are described. In the first experiment, total differential cross sections are measured for collisions between two methane molecules. Treating the scattering as elastic, these cross sections are used to determine an isotropic intermolecular potential energy function for the methane-methane system. The second experiment involves the measurement of total differential cross sections and time-of-flight spectra for neon-chlorine scattering. These data are modeled using the infinite order sudden approximation for rotationally inelastic scattering, and an anisotropic potential function for neon-chlorine is determined. In the third experiment, the angular and time-of-flight distributions for the products of the three-body photofragmentation of 1,2-diiodotetrafluoroethane at 266 nm are measured. These data are analyzed to determine the product translational energy distributions.
", "doi": "10.7907/xz77-2x37", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:5980", "collection": "thesis", "collection_id": "5980", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07262010-154826937", "primary_object_url": { "basename": "Kang_h_1986.pdf", "content": "final", "filesize": 3745219, "license": "other", "mime_type": "application/pdf", "url": "/5980/1/Kang_h_1986.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Gas Phase Studies of Hydrocarbon Oxidation by Chromium Oxide Cation", "author": [ { "family_name": "Kang", "given_name": "Heon", "clpid": "Kang-Heon" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "An ion beam reactive scattering technique is used to study organometallic reactions in the gas phase. Detailed investigations of the reactions of CrO+ with hydrocarbons are reported. CrO+ formed by surface ionization oxidizes both alkenes and alkanes larger than methane with a high degree of selectivity compared with other first-row transition metal oxides. Analyses of reaction energetics are facilitated by determination of ancillary thermochemical data, including Cr+-O and CrO+-H bond dissociation energies.
\r\n\r\nChapter II presents an analysis of the reactions of CrO+ with alkenes. Major reaction channels include allylic hydrogen abstraction by CrO+ and oxidative cleavage of double bonds to form aldehydes and smaller alkenes.
\r\n\r\nChapter III describes selective oxidation of saturated hydrocarbons by CrO+. Major product channels include alcohol formation, dehydrogenation, and loss of alkanes and alkenes. Reaction intermediates in which alkyl C-H bonds add across the Cr+-O bond are proposed.
\r\n\r\nChapter IV presents studies of reactions of transition metal ions (Ti, V, Cr, Fe, Co, and Ni) with organosilanes in the gas phase. These reactions often lead to formation of metal silylenes as major products. An examination of reaction thermochemistry provides estimates for metal-silylene bond dissociation energies. Relationships between the reactivities, metal-silylene bond energies, and the electronic structures of the metal ions are discussed.
\r\n\r\nChapter V describes a novel source which generates metal atom and ion beams by focusing a CO2 TEA laser onto a solid metal target. Kinetic energy distributions of laser-generated atoms and atomic ions are measured using time-of-flight techniques. Possible mechanisms for the metal ion production as well as aspects of employing the laser-generated beams for gas phase reaction studies are discussed.
", "doi": "10.7907/M9HQ-9749", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:8074", "collection": "thesis", "collection_id": "8074", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02132014-084828083", "type": "thesis", "title": "Variable-Angle Electron Spectroscopic Studies of Various Polyatomic Molecular Systems", "author": [ { "family_name": "Koerting", "given_name": "Charles Frederick", "clpid": "Koerting-Charles-Frederick" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The complementary techniques of low-energy, variable-angle electron-impact spectroscopy and ultraviolet variable-angle photoelectron spectroscopy have been used to study the electronic spectroscopy and structure of several series of molecules. Electron-impact studies were performed at incident beam energies between 25 eV and 100 eV and at scattering angles ranging from 0\u00b0 to 90\u00b0. The energy-loss regions from 0 eV to greater than 15 eV were studied. Photoelectron spectroscopic studies were conducted using a HeI radiation source and spectra were measured at scattering angles from 45\u00b0 to 90\u00b0. The molecules studied were chosen because of their spectroscopic, chemical, and structural interest. The operation of a new electron-impact spectrometer with multiple-mode target source capability is described. This spectrometer has been used to investigate the spin-forbidden transitions in a number of molecular systems.
\r\n\r\nThe electron-impact spectroscopy of the six chloro-substituted ethylenes has been studied over the energy-loss region from 0-15 eV. Spin-forbidden excitations corresponding to the \u03c0 \u2192 \u03c0*, N \u2192 T transition have been observed at excitation energies ranging from 4.13 eV in vinyl chloride to 3.54 eV in tetrachloroethylene. Symmetry-forbidden transitions of the type \u03c0 \u2192 np have been oberved in trans-dichloroethyene and tetrachlor oethylene. In addition, transitions to many states lying above the first ionization potential were observed for the first time. Many of these bands have been assigned to Rydberg series converging to higher ionization potentials. The trends observed in the measured transition energies for the \u03c0 \u2192 \u03c0*, N \u2192 T, and N \u2192 V as well as the \u03c0 \u2192 3s excitation are discussed and compared to those observed in the methyl- and fluoro-substituted ethylenes.
\r\n\r\nThe electron energy-loss spectra of the group VIb transition metal hexacarbonyls have been studied in the 0 eV to 15 eV region. The differential cross sections were obtained for several features in the 3-7 eV energy-loss region. The symmetry-forbidden nature of the 1A1g \u2192 1A1g, 2t2g(\u03c0) \u2192 3t2g(\u03c0*) transition in these compounds was confirmed by the high-energy, low-angle behavior of their relative intensities. Several low lying transitions have been assigned to ligand field transitions on the basis of the energy and angular behavior of the differential cross sections for these transitions. No transitions which could clearly be assigned to singlet \u2192 triplet excitations involving metal orbitals were located. A number of states lying above the first ionization potential have been observed for the first time. A number of features in the 6-14 eV energy-loss region of the spectra of these compounds correspond quite well to those observed in free CO.
\r\n\r\nA number of exploratory studies have been performed. The \u03c0 \u2192 \u03c0*, N \u2192 T, singlet \u2192 triplet excitation has been located in vinyl bromide at 4.05 eV. We have also observed this transition at approximately 3.8 eV in a cis-/trans- mixture of the 1,2-dibromoethylenes. The low-angle spectrum of iron pentacarbonyl was measured over the energy-loss region extending from 2-12 eV. A number of transitions of 8 eV or greater excitation energy were observed for the first time. Cyclopropane was also studied at both high and low angles but no clear evidence for any spin-forbidden transitions was found. The electron-impact spectrum of the methyl radical resulting from the pyrolysis of tetramethyl tin was obtained at 100 eV incident energy and at 0\u00b0 scattering angle. Transitions observed at 5.70 eV and 8.30 eV agree well with the previous optical results. In addition, a number of bands were observed in the 8-14 eV region which are most likely due to Rydberg transitions converging to the higher ionization potentials of this molecule. This is the first reported electron-impact spectrum of a polyatomic free radical.
\r\n\r\nVariable-angle photoelectron spectroscopic studies were performed on a series of three-membered-ring heterocyclic compounds. These compounds are of great interest due to their highly unusual structure. Photoelectron angular distributions using HeI radiation have been measured for the first time for ethylene oxide and ethyleneimine. The measured anisotropy parameters, \u03b2, along with those measured for cyclopropane were used to confirm the orbital correlations and photoelectron band assignments. No high values of \u03b2 similar to those expected for alkene \u03c0 orbitals were observed for the Walsh or Forster-Coulson-Moffit type orbitals.
", "doi": "10.7907/YP9D-ED80", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11383", "collection": "thesis", "collection_id": "11383", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02052019-112244749", "primary_object_url": { "basename": "Flanagan_DJ_1985.pdf", "content": "final", "filesize": 85214194, "license": "other", "mime_type": "application/pdf", "url": "/11383/1/Flanagan_DJ_1985.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Angular Resolved Photoelectron Spectroscopy of Various Polyatomic Molecular Systems", "author": [ { "family_name": "Flanagan", "given_name": "Dorothy Jean", "clpid": "Flanagan-Dorothy-Jean" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis describes the study of the angular resolved photoelectron spectroscopy of a series of polyatomic molecules. The spectrometer consists of a He I radiation source, a scattering chamber, and a rotatable detection system which includes a set of electrostatic lenses, a hemispherical electrostatic kinetic energy analyzer and an electron multiplier. Angular distributions are determined from the variation in intensity as the detection system is rotated about the center of the scattering chamber.
\r\n\r\nThe theory of photoionization is discussed semiclassically, as the interaction of an atom or molecule treated quantum mechanically with a classical radiation field. Some recent calculations of the asymmetry parameter for valence electrons are briefly reviewed.
\r\n\r\nPhotoelectron angular distributions were measured for acetylene, propyne, 1-butyne, and 2-butyne. The asymmetry parameters of propyne, 1-butyne, and 2-butyne have been determined for the first time. Trends in the asymmetry parameter, ionization potentials and band shapes were studied. It was determined that the parity favoredness rules of Chang failed to account for the behavior of the asymmetry parameter of the molecule despite the symmetry of the molecule. Instead, acetylene and its alkylated analogs follow the trends in \u03b2 observed in studies of the methylated ethenes.
\r\n\r\nAdditionally, the semi-empirical rule that the \u03b2 values of \u03c0 orbitals are higher than for \u03c3 orbitals was violated in this series. Acetylene and propyne possess \u03c3 orbital with \u03b2 values significantly higher than the \u03c0 orbitals.
\r\n\r\nTwo principal substituent effects were observed: 1) a systematic decrease in the first ionization potential and 2) a similar decrease in the asymmetry parameter of the X̃ band with increasing alkylation.
\r\n\r\nThe photoelectron angular distributions were measured for formaldehyde, acetaldehyde, and acetone. The asymmetry parameter has been determined for the first time for acetaldehyde, and, with the exception of the first band, for acetone.
\r\n\r\nThis study has shown that the beta values of the X̃ nO bands of these molecules are, within experimental error, invariant with respect to methyl substitution, results that are consistent with the nonbonding characteristics of the molecular orbitals. The à \u03c0C = O bands, however, show a strong decrease in the asymmetry parameter of approximately 0.2 per methylation in a manner similar to that observed previously in the methylated ethenes and ethynes. The expected systematic decrease in first ionization potential with substitution was also observed.
\r\n\r\nLastly, HAM/3 calculations were performed to determine the ionization potentials of some substituted carbonyls and to examine the excitation energies of ethylene and its methyl and fluoro derivatives to evaluate the method's usefulness to studies in electron impact spectroscopy.
\r\n\r\nThere was generally good agreement between the ionization potential calculated by this method and experimentally determined values. Agreement between the calculated values of the excitation energies and the experimental were reasonable but the method was not sensitive enough to reproduce the trends observed with increasing substitution of the chromophore.
", "doi": "10.7907/f9mq-vz30", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:6819", "collection": "thesis", "collection_id": "6819", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02132012-111043915", "type": "thesis", "title": "The Production and Characterization of an Intense Hyperthermal Beam of H\u2083 Molecules and of H Atoms", "author": [ { "family_name": "Garvey", "given_name": "James F.", "clpid": "Garvey-James-F" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The simplest bimolecular reaction involving neutral reagents is the reaction
\r\n\r\nH + H2 \u2192 H2 + H.
\r\n\r\nThis system, because of its simplicity and fundamental significance in chemical dynamics, has been the subject of extensive accurate ab initio theoretical quantum mechanical calculations and the results obtained have been used to test approximate theories of reaction dynamics. However, this system has proved difficult to study experimentally due to its high activation barrier (~ .33 eV) and its small reactive cross section (~ 1 x 10-16 cm2. Because of these factors, state-to-state reaction dynamics have only become feasible recently.
\r\n\r\nIn order to study this reaction in a crossed molecular beam experiment, a means of generating an intense beam of H atoms is essential. This thesis documents the design and operation of a hydrogen arc discharge for generating such a beam. The method consists of using a high power arc discharge to create a high temperature (~ 12,000 K) plasma in which H2 molecules can be dissociated into atoms. By using an arc source of the type developed by Kunth, a stable, intense, hyperthermal H atom beam has been successfully produced. Section 2 of this thesis discusses the design and operation of the apparatus and Section 3 of the thesis discusses the characterization of the hydrogen atoms within the beam. The laboratory energy distribution function of these atoms was determined approximately, and spans the range from 0.5 eV to about 12 eV. The total intensity of this beam is of the order of ~1022 atoms/sterad/sec. With such an intense and energetic beam, a wealth of chemical dynamical experiments may now become feasible.
\r\n\r\nIn the course of developing this intense beam of hydrogen atoms, the source was found to also produce metastable H3 molecules. This is the first direct, unambiguous observation of such a specie in a molecular beam, and is discussed in Section 4. Translational energy analysis of this H3 molecule indicates an energy distribution similar to that of the H atoms, suggesting that the lifetime of H3 is of the order of 40 \u00b5sec or longer. We also observed emission spectra from the Rydberg states of H3 identified previously by Herzberg. This is spectroscopic evidence for the presence of this neutral molecule in our beam. The only know state of H3 capable of having the long lifetime observed is 2p 2A\"2, the second excited state of this species.
\r\n\r\nIn addition, we detected this molecule by a variety of other independent techniques. It has long been known that alkali metal atoms with low ionization potential will ionize upon collision with a metal surface having a high work function. The 2p 2A\"2 state of H3 has an IP of ~ 3.7 eV and is expected to behave in a similar way. As a result, surface ionization of metastable 3 has been observed for for a variety of metals and is reported in this thesis. From that low IP one would also expect that the metastable H3 should be photoionizable using an appropriate light source. In this thesis we report the generation of H+3 through irradiation of the beam with the light from a high intensity mercury lamp. Lastly, since the metastable H3 is in a Rydberg state, it would be expected to exhibit a large total scattering cross section due to the diffuse nature of the Rydberg orbital. Such cross sections were measured by the attenuation of the H3 beam as it passed through a gas cell.
\r\n\r\nSection 5 describes the first observation of the electronic spectrum of WH. This emission spectrum was due to WH formed by the presence of the tungsten anode and cathode which are heated too close to its melting point by the arc discharge. Analysis of this spectrum has given rotational constants and bond distances for the electronic states of the mono-hydride involved in the observed transisiton. Due to relativistic terms in the potential, the theoretical calculation of WH has proved difficult to date. Recently a reliable potential for W has been generated such that our experimental bond distances will provide an important empirical check for any further theoretical calculations performed on this system. Likewise, the arc source may be employed in the future as a means of generating new metal hydride emission spectra.
\r\n\r\nAppendix A of the thesis details the design and construction of the inhomogeneous magnet to serve in the future as a velocity selector for the hyperthermal hydrogen beam in our crossed beam experiment. Using such a Stern-Gerlach magnet as a velocity selector, the dynamics of the H + H2 reaction can be probed as a function of translational energy of the reactants. Appendix B grew out of an interesting Ch 227 project and will now become a theoretical paper. Exact quantum mechanical calculations of the collinear reaction Be + FH (\u03bd = 0, 1) have been performed and the effects of reagent translational and vibrational excitation on reaction probabilities and product state distributions are examined. These quantum mechanical results are compared with those of quasi-classical trajectory calculations reported previously.
", "doi": "10.7907/r4n1-8762", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11350", "collection": "thesis", "collection_id": "11350", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01222019-123545387", "primary_object_url": { "basename": "Winniczek_JW_1985.pdf", "content": "final", "filesize": 110565437, "license": "other", "mime_type": "application/pdf", "url": "/11350/1/Winniczek_JW_1985.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Anisotropic Interaction Potentials between Helium and Linear Molecules from Crossed Beam Experiments", "author": [ { "family_name": "Winniczek", "given_name": "Jaroslaw W.", "clpid": "Winniczek-Jaroslaw-W" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Anisotropic interaction potentials between helium and linear molecules have been studied experimentally and theoretically to examine the relationship between the potential and the scattering differential cross-section, and to extract these potentials from crossed-molecular beam data.
\r\n\r\nChapter 2 presents the measurement of total (elastic and inelastic) differential scattering cross sections for He + CO2, CS2, OCS at a relative collision energy of about 65 meV with a crossed molecular beam apparatus. Anisotropic interaction potentials were extracted from these data, by way of an infinite order sudden approximation analysis. Several different anisotropic potential models were used in this analysis. The necessity for considering the anisotropy in the position of the well minimum as well as of its depth is demonstrated. A potential is proposed for He + OCS that reflects the symmetry of OCS, with a minimum number of modeling parameters.
\r\n\r\nIn Chapter 3 a detailed sensitivity analysis of the total and rotational state-to-state differential cross-section (DCS) is performed on an empirical potential energy surface for He + CO2. The infinite order sudden approximation is used to calculate the cross-sections. The sensitivity analysis consists of: 1) a large scale modification of the parameters that determine the anisotropic potential, and 2) an infinitesimal variation of these parameters to obtain a relative sensitivity function for the DCS. From these we demonstrate the effect each potential parameter has on the cross-sections. Despite the fact that this highly quantum system displays no classical effects such as rainbow scattering, we have shown that the quantal DCS oscillations contain significant information regarding the depth and width of the potential well and its anisotropy. Much of this information can be extracted from total-DCS scattering data. However the rotationally inelastic DCS contain a substantial amount of additional information regarding the shape of the potential energy surface.
\r\n\r\nSome of the conclusions reached in Chapter 3 indicate that the measuring of rotationally inelastic differential cross-sections can provide significantly greater insight into the nature of the potential than does the total DCS. In Chapter 4 we develop the means for simulating experimentally observable data from the potential for a given set of apparatus conditions. In Chapter 5 we describe modifications made to the crossed-beam apparatus in order to observe this inelasticity and present preliminary results for He + CO2.
", "doi": "10.7907/5nvw-ym37", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:8597", "collection": "thesis", "collection_id": "8597", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-143633362", "primary_object_url": { "basename": "BOLAND_JJ_1985.pdf", "content": "final", "filesize": 5267851, "license": "other", "mime_type": "application/pdf", "url": "/8597/1/BOLAND_JJ_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Experimental and Theoretical Developments in Extended X-Ray Absorption Fine Structure (EXAFS) Spectroscopy", "author": [ { "family_name": "Boland", "given_name": "John James", "clpid": "Boland-John-James" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "McGill", "given_name": "Thomas C.", "clpid": "McGill-T-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "To obtain accurate information from a structural tool it is necessary to have an understanding of the physical principles which govern the interaction between the probe and the sample under investigation. In this thesis a detailed study of the physical basis for Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is presented. A single scattering formalism of EXAFS is introduced which allows a rigorous treatment of the central atom potential. A final state interaction formalism of EXAFS is also discussed. Multiple scattering processes are shown to be significant for systems of certain geometries. The standard single scattering EXAFS analysis produces erroneous results if the data contain a large multiple scattering contribution. The effect of thermal vibrations on such multiple scattering paths is also discussed. From symmetry considerations it is shown that only certain normal modes contribute to the Debye-Waller factor for a particular scattering path. Furthermore, changes in the scattering angles induced by thermal vibrations produces additional EXAFS components called modification factors. These factors are shown to be small for most systems.
\r\n\r\nA study of the physical basis for the determination of structural information from EXAFS data is also presented. An objective method of determining the background absorption and the threshold energy is discussed and involves Gaussian functions. In addition, a scheme to determine the nature of the scattering atom in EXAFS experiments is introduced. This scheme is based on the fact that the phase intercept is a measure of the type of scattering atom. A method to determine bond distances is also discussed and does not require the use of model compounds or calculated phase shifts. The physical basis for this method is the absence of a linear term in the scattering phases. Therefore, it is possible to separate these phases from the linear term containing the distance information in the total phase.
\r\n", "doi": "10.7907/YGM3-F114", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11249", "collection": "thesis", "collection_id": "11249", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10262018-123200794", "primary_object_url": { "basename": "Casassa_MP_1984.pdf", "content": "final", "filesize": 72224775, "license": "other", "mime_type": "application/pdf", "url": "/11249/1/Casassa_MP_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Infrared Photodissociation of Van der Waals Molecules", "author": [ { "family_name": "Casassa", "given_name": "Michael Paul", "clpid": "Casassa-Michael-Paul" } ], "thesis_advisor": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "thesis_committee": [ { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Samson", "given_name": "Sten Otto", "clpid": "Samson-Sten-Otto" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Infrared photodissociation of van der Waals molecules is investigated using low power cw infrared lasers. Information gained concerns the dynamics of vibrational predissociation and the van der Waals interactions. Clusters formed in supersonic molecular beams are irradiated for approximately 0.5 msec and the fraction of clusters remaining intact is measured as a function of laser wavelength and power. Detailed homogeneous and inhomogeneous line shape models are presented and used to analyze the results. Effects such as fluence broadening and orientational inhomogeneity are described.
\r\n\r\nVan der Waals molecules studied include dimeric clusters of ethylene with rare gases, hydrogen halides and non-hydrogen bonding polyatomic molecules. Homogeneous widths of clusters excited near the \u03bd7 frequency of free ethylene correspond to lifetimes ranging from 0. 44 psec for (C2H4)2 to greater than 10 psec for Ne\u2022C2H4. These are attributed to vibrational predissociation constrained by conservation of angular momentum. Other conceivable broadening mechanisms are discussed.
\r\n\r\nSpectra obtained by exciting the \u03bd7 mode in different types of ethylene clusters are quite dissimilar. Lineshape analysis indicates that the \u03bd7 transition in (C2H4)2 occurs as a hybrid band. The same transition in (C2H4\u00b7HF occurs as a perpendicular band. The rare gas-ethylene clusters are less rigid than the others and excitation of hindered internal rotation of C2H4 accompanies the \u03bd7 absorption. All of the ethylene clusters exhibit blue shifts and intensity enhancement, as compared to \u03bd7 absorption by free ethylene, which are attributed largely to electrostatic interactions.
\r\n", "doi": "10.7907/n43s-1339", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11251", "collection": "thesis", "collection_id": "11251", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10292018-120530235", "primary_object_url": { "basename": "Banerjee_U_1984.pdf", "content": "final", "filesize": 63119892, "license": "other", "mime_type": "application/pdf", "url": "/11251/1/Banerjee_U_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Alamethicin: Secondary Structure in Solution and Interactions with Phospholipid Membranes", "author": [ { "family_name": "Banerjee", "given_name": "Utpal", "clpid": "Banerjee-Utpal" } ], "thesis_advisor": [ { "family_name": "Hopfield", "given_name": "John J.", "clpid": "Hopfield-J-J" } ], "thesis_committee": [ { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Davidson", "given_name": "Norman R.", "clpid": "Davidson-N-R" }, { "family_name": "Hopfield", "given_name": "John J.", "clpid": "Hopfield-J-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The icosapeptide alamethicin [sequence included in scanned thesis' abstract, p. v] isolated from the fungus Trichoderma viride induces voltage-gated ionic conductance in black lipid film membranes (Latorre, R. & Alvarez, D. (1981) Physiol. Rev. 61, 77). Single-channel measurements have indicated that passive ion transport across membranes is mediated by alamethicin channels that fluctuate between several conduction states. While these studies provide phenomenological description of the nature of alamethicin-assisted ionic conduction, very few studies probed the molecular structure of this peptide and the nature of its interaction with lipid membranes. These issues are addressed in the present investigation.
\r\n\r\nAn analysis of the proton magnetic resonance spectrum is undertaken. Two-dimensional NMR is employed to achieve a complete assignment of the protons in the molecule to NMR resonances. The spectral assignment is a necessary first step towards molecular interpretations.
\r\n\r\nMeasurement of coupling constants and two-dimensional NOE's suggest a half-helical, half-extended dimeric structure for the molecule in methanol. This proposed model for the secondary structure, consistent with the NMR data as well as a line of other experimental observations erstwhile published, predicts that (a) the amide protons of residues 15 through 20 are intermolecularly hydrogen-bonded with the corresponding residues of the opposing molecule to create a rigid, extended parallel \u03b2-pleated structure for the C-terminal end of the molecule; (b) the proline at position 14 breaks the continuity of this structure, and amino acids 10 through 14 are forced into an open, non-hydrogen-bonded conformation, and (c) amino acids 3 through 9 are folded into an \u03b1-helix, with Gln-7 side chains from the two strands in the right juxtaposition to facilitate a hydrogen bond between them. The resultant structure is highly amphipathic: one face is completely hydrophobic with the aliphatic side chains exposed, whereas the other face is primarily hydrophilic with polar side chains and peptide groups lining the extended \u03b2-sheet region.
\r\n\r\nThe dimeric structure is further supported by relaxation measurements that indicate that the N-acetyl methyl groups at the N-termini of the two helices in the dimer have distinct proton spin-spin relaxation times. This difference is eliminated once the dimers are dissociated with urea.
\r\n\r\nSpectral assignments in water are complicated by broadened NMR signals due to aggregation. Standard two-dimensional and decoupling techniques for assignments are inadequate for this case. A successful assignment is achieved by solvent titration from methanol. No changes in coupling constants are noted during the titration, and it is expected that the conformation in water is similar if not identical, to that in methanol. Relaxation measurements in water are consistent with a tightly bound dimeric unit that micellises to larger aggregates.
\r\n\r\nThe interaction of alamethicin with multilayers is inferred from a spectroscopic investigation of the phospholipid bilayer prepared from dimyristoyllecithin (DML) in the presence and absence of alamethicin, and, for contrast, in the presence of other membrane active molecules. The dynamics and conformation of phospholipid head group and chains are examined by P31 and H2 NMR. A P31 line shape calculation has helped identify the dependence of the spectrum on various motional, relaxation and conformational parameters.
\r\n\r\nAs part of the investigation of lipid packing and dynamics in membranes, small bilayer vesicles are also studied. Proton NMR indicates that the outside-facing and inside-facing leaflets of the bilayer in small vesicles have lipids packed in different densities. This is due to the differences in the extent and sign of curvature of the two leaflets. At the high field at which this NMR study is undertaken, the differences in packing show up as distinct proton peaks from the inside and outside chain methylene and methyl groups nthat differ in width and in chemical shift.
\r\n\r\nFinally, the interaction of alamethicin with DML multilayers is characterized by P31, H2 and H1 NMR and Raman spectroscopy. The reduction in chemical shift anisotropy (\u0394\u03c3) of the P31 signal is interpreted in terms of an interaction of the peptide at the water-membrane interface that causes a change in the average head group orientation. Deuterium NMR shows no changes in quadrupolar splittings (and hence C-D order parameters) of the chain deuterons, and Raman spectroscopy shows no change in the gauche-trans ratio of methylene segments in the chain. These results are contrasted with P31 and H2 NMR of the gramicidin S/DML system that shows polymorphism due to partial disruption of the multilayer structure and the chlorophyll A/DML system that exhibits a 7\u00b0 C change in phase transition temperature as a clear indication of incorporation of the phytol chain into the bilayer.
\r\n\r\nTaken together, these experiments unequivocally indicate that the peptide interacts with lipid bilayers at the lipid-water interface. The proposed amphiphilic aggregated solution structure for the peptide is ideally suited for such an interaction. Inasmuch as the conductance characteristics of alamethicin are only explained in terms of transmembrane pore formation, it is proposed that the large dipole moment of this aggregate facilitates the transfer of the peptide into the bilayer once a gradient of field is applied.
\r\n", "doi": "10.7907/9y1x-zh89", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11838", "collection": "thesis", "collection_id": "11838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10212019-175021360", "type": "thesis", "title": "One- and Two-Color Laser Spectroscopy with Photoacoustic and Multiphoton Ionization Detection", "author": [ { "family_name": "Moll", "given_name": "David Jerry", "clpid": "Moll-David-Jerry" } ], "thesis_advisor": [ { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The techniques of pulsed photoacoustic spectroscopy and multiphoton ionization spectroscopy have been used to study several types of weak optical transitions in the ultraviolet or visible spectral regions for gas phase molecules. Both one- and two-color experiments have been performed. The one-color experiments involved the study of high vibrational overtones and spin-forbidden transitions. The two-color experiments demonstrated the application of photoacoustic detection of stimulated emission pumping for populating high vibration levels of the ground electronic state. Two-color experiments were also used to study excited state absorption processes in aniline.
\r\n\r\nPulsed laser photoacoustic spectra of CD3H in the region of the \u2207vCH = 5, 6, and 7 CH stretch overtones were obtained. These overtones and nearby combination bands displayed sharp rotational structure, indicating a minimum excited state population relaxation time of 5 x 10-12 sec. A combination sum analysis was used to generate excited state rotational constants B'. These constants reflect the geometries of the excited states, and therefore provide a sensitive probe of the mixing between various zero order excited states.
\r\n\r\nPhotoacoustic detection was used to monitor a stimulated emission pumping process in p-difluorobenzene. Using the Ã1B2u 5' state as an intermediate state, several vibrational levels of the ground electronic state were populated. The photoacoustic technique is an attractive alternative to other techniques because of its sensitivity, simplicity, and its ability to differentiate between stimulated emission pumping and excited state absorption.
\r\n\r\nTime-resolved excited state absorption studies were performed on aniline using the multiphoton ionization and photoacoustic detection techniques. Signals from both of these techniques were measured as a function of the time delay between two laser pulses of different wavelength. The first pulse excited the S1 0-0 transition. The second pulse excited either S1 or a triplet state produced by intersystem crossing, depending on the time delay between pulses. Both ionization and dissociation processes were observed. By varying the conditions of excitation, it appears that a given amount of energy can be selectively channeled into either ionization or dissociation pathways. These results were explained using a simple Franck Condon factor model.
\r\n\r\nThe application of pulsed laser photoacoustic spectroscopy to the study of weak absorptions in the visible and ultraviolet spectral regions was investigated. Photoacoustic spectra of triplet states in CS2, SO2, biacetyl, and thiophosgene were obtained. An attempt to detect the ã3B1u state in benzene, produced instead a two-photon spectrum of several Rydberg states. It was discovered that the sensitivity of the pulsed photoacoustic technique for extremely weak absorptions is limited by the increased probability of multiphoton absorption when high intensities are used.
\r\n\r\nFinally, in two appendices, the detection of the ã3A2 state in CS2 by the multiphoton ionization technique is presented. The CS2 study demonstrates the utility of the multiphoton ionization technique for detecting spin-forbidden transitions at high resulution and with great sensitivity.
", "doi": "10.7907/60wm-py84", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3840", "collection": "thesis", "collection_id": "3840", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-132833", "type": "thesis", "title": "Studies of Chemical Adsorption Using Low-Energy Electron Diffraction", "author": [ { "family_name": "Williams", "given_name": "Ellen D.", "clpid": "Williams-Ellen-D" } ], "thesis_advisor": [ { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "thesis_committee": [ { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" } ], "local_group": [ { "literal": "Caltech Distinguished Alumni Award" }, { "literal": "div_chem" } ], "abstract": "Both experimental and computational studies based on low-energy electron diffraction (LEED) have been performed to determine the nature of order in chemically adsorbed overlayers. These studies have been directed towards obtaining a better understanding of adatom-adatom interactions by measurement of their most obvious manifestations; change in overlayer order during adsorption and co-adsorption, island formation, and order-disorder phenomena.
\r\n\r\nThe effect of the co-adsorption of hydrogen on the ordering of CO on Rh(111) has been studied using LEED and thermal desorption mass spectrometry. The results indicate that the adsorption of CO proceeds via a physically adsorbed intermediate. In addition, there is a strong repulsive interaction between CO molecules and hydrogen atoms co-adsorbed on Rh(111). This interaction is apparent at distances up to 2.7-3.1 \u00c5 indicating that it is a through-metal effect.
\r\n\r\nA series of LEED patterns has been observed during the adsorption of sulfur on the reconstructed IR(110)-(1x2) surface. The structure observed at lowest coverages has a p2mg symmetry. This allows a determination of the absolute coverage, and indicates a probable binding site for the sulfur atoms.
\r\n\r\nA Monte Carlo simulation of the order-disorder behavior of oxygen on W(110) has been performed. General expressions relating the values of the interaction energies to the transition temperatures for a lattice gas with first, second and third neighbor interactions have been determined. Symmetry considerations in selecting a model for the interaction energies are discussed.
\r\n\r\nThe effect of the ordering of adsorbed molecules into small islands on the LEED beam profile has been determined. In the limit of a random distribution of island positions the overall intensity is shown to be the weighted sum of the intensities from the individual islands. Computer simulations of island-containing overlayers have been used to determine the effect on the beam profiles of deviations from a random distribution of islands.
\r\n\r\nExperimental studies of island formation for CO on Ru(001) have been performed. The finite size of the ordered islands has a strong effect on the order-disorder behavior. Quantitative measurements of this effect have allowed a determination of the island size distribution and thus, the mean island size as a function of coverage.
\r\n", "doi": "10.7907/DYY3-MQ42", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:5390", "collection": "thesis", "collection_id": "5390", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11192009-134206825", "type": "thesis", "title": "Electronic Transitions of Molecules by Electron Impact and Multiphoton Ionization Spectroscopy", "author": [ { "family_name": "Rianda", "given_name": "Ronald", "clpid": "Rianda-Ronald" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The experimental work discussed in this thesis is concerned primarily with the detection of electric dipole forbidden transitions of molecules in the gas phase. The thesis is divided into two parts. The first part describes measurements made using the technique of low-energy, variable-angle, electron impact spectroscopy. The second part describes investigations performed using resonance enhanced multiphoton ionization (REMPI) spectroscopy.
\r\n\r\nThe low-energy variable-angle electron impact technique has been used to study the electronic spectroscopy of molecules. Both dipole allowed and dipole forbidden transitions have been investigated. Transitions having excitation energies from 0 eV to 20 eV have been studied using incident electron beam energies ranging from 25 eV to 75 eV and scattering angles from 0\u00b0 to 80\u00b0. Molecules studied included nitric oxide (NO), uranium hexafluoride (UF6), tungsten hexafluoride (WF6), nitrogen dioxide (NO2), hydrogen cyanide (HCN), acetonitrile (CH3CN), propionitrile (C2H5CN), butyronitrile (C3H7CN), and malononitrile (CH2(CN)2).
\r\n\r\nWeak structure was observed in the spectrum of nitric oxide between 5.22 eV and 5.60 eV. These bands have been assigned as vibronic bands belonging to the X2\u03c0 \u2192 a4\u03c0 transition. Additional structure extending from 5.7 eV to about 7 eV was assigned to the X2\u03c0 \u2192 b4\u03a3- transition. Several higher lying transitions were observed which have been tentatively assigned as doublet \u2192 quartet in nature.
\r\n\r\nIn order to elucidate the electronic structure of uranium hexafluoride the electron impact spectra at UF6 and WF6 were determined. Eleven features were observed in UF6 with intensity maxima at 3.26, 4.2, 4.7, 5.8, 7.0, 7.86, 9.26, 11.01, 11.75, 12.5 and 13.2 eV. Features were observed in the spectrum at 7.25, 7.9, 8.5, 9.85, 11.75, 12.6 and 13.5 eV. Comparison of the spectra indicate that the primary contribution to transition intensity in UF6 above 5.8 eV and in WF6 results form charge transfer excitations from fluorine p orbitals to metal d orbitals. Tentative assignments based on previous theoretical studies are made.
\r\n\r\nA previously unreported doublet \u2192 quartet transition was observed at 4.49 eV in the electron impact spectrum of NO2, in excellent agreement with theoretical calculations. Doublet \u2192 doublet transitions were observed with maxima at 2.95, 5.81, 7.48, 8.64, 9.69, 10.52, 10.68, 10.94 and 11.20 eV in agreement with previous studies.
\r\n\r\nThe series of C \u039e N containing molecules, Aydrogen cyanide, acetonitrile, malononitrile, propionitrile and butyronitrile, have also been studied using the electron impact technique. Results for hydrogen cyanide are in excellent agreement with previous work. Previously undetected singlet \u2192 triplet transitions of acetonitrile, propionitrile and butyronitrile are reported. In addition the first study of the electronic spectrum of malononitrile is reported.
\r\n\r\nTwo appendices to Part One are included. The first of these reports the results of generalized valence bond and configuration interaction studies of the low lying states of ammonia. The second appendix discusses an electron impact study of the electronically excited states of 1,3,5-cycloheptatriene.
\r\n\r\nPart Two of this thesis describes the theory of multiphoton ionization and reports results obtained using this technique. The application of REMPI spectroscopy to the detection of spin forbidden transitions is examined. It is shown in a study of the X1\u03a3+g \u2192 a3A2 state of CS2 to offer potential for the detection of spin forbidden transitions at high resolution and with great sensitivity.
\r\n\r\nFinally a preliminary study of the two-photon resonance enhanced multiphoton ionization of p-xylene is reported. Several elements of the X1Ag \u2192 1B2u transition observed previously in benzene and p-difluorobenzene are reported.
\r\n", "doi": "10.7907/b7ed-jg16", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:6823", "collection": "thesis", "collection_id": "6823", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02152012-151600900", "type": "thesis", "title": "Theoretical Studies of Chemical Reaction Dynamics", "author": [ { "family_name": "Kaye", "given_name": "Jack Alan", "clpid": "Kaye-Jack-Alan" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" }, { "family_name": "Sparks", "given_name": "Randal K.", "clpid": "Sparks-Randal-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The collinear collision of an atom with a diatomic molecule has been studied within the frameworks of quantum and classical mechanics. Three major topics have been investigated.
\r\n\r\nIn part I, the collinear collision of hydrogen atoms with hydrogen fluoride (and singly deuterium substituted variants of this system) have been studied in the exchange channel by coupled-channel quantum mechanical calculations using a realistic (high barrier) potential energy surface. We have also investigated the effect on the dynamics of varying the barrier height of the potential energy surface.
\r\n\r\nIn part II, we consider the characterization of low energy resonances in the collinear H + H2 and F + H2(HD, DH, D2) systems. A variety of characterization techniques are used; the most useful proves to be the variation with energy of the eigenvalues of the collision lifetime matrix.
\r\n\r\nIn part III, we develop the method of hyperspherical coordinates for the study of collinear reactive atom-diatomic molecule collisions. The method is tested for the H + H2 system, and is applied to a model system above the threshhold for collision-induced dissociation and to reactions in which a light atom (hydrogen) is transferred between two heavy ones. Systems of this type studied include I + HI and Br + HCl; we also consider some aspects of the dynamics in the Cl + HCl system. We develop the formalism to extract the physical scattering wave function from the method and present preliminary results of probability densities and probability current densities on the H + H2 system. We also consider the formulation of the method in the adiabatic representation and examine both numerically and analytically the behavior of the coupling matrices at large values of the propagation variable. Convergence properties of the method are investigated in detail for the H + H2 and F + H2 systems. Quasi-classical trajectory calculations have been used to help understand the results obtained and to determine the importance of quantum mechanical effects.
\r\n", "doi": "10.7907/vkds-vb56", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:10778", "collection": "thesis", "collection_id": "10778", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03222018-134525550", "primary_object_url": { "basename": "Thiel_PA_1981.pdf", "content": "final", "filesize": 148736950, "license": "other", "mime_type": "application/pdf", "url": "/10778/1/Thiel_PA_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Adsorption, Co-Adsorption and Catalytic Reactions on Rh(111) and Ru(001) Surfaces", "author": [ { "family_name": "Thiel", "given_name": "Patricia Ann", "clpid": "Thiel-Patricia-Ann" } ], "thesis_advisor": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "thesis_committee": [ { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The adsorption of oxygen, hydrogen, carbon monoxide , nitric oxide and water on Rh(111) and Ru(001) surfaces has been studied using the techniques of high-resolution electron energy loss spectroscopy, low-energy electron diffraction, Auger electron spectroscopy, ultraviolet photoelectron spectroscopy and thermal desorption mass spectrometry. In many cases co-adsorption experiments have provided insight into the nature of interaction between different adsorbates, with potential implications for heteroqeneous catalytic reaction mechanisms.
\r\n\r\nThe interaction of oxygen with Rh(111) consists of adsorption, irreversible thermally induced ordering and disordering phenomena, dissolution into the subsurface region and desorption. The thermodynamic parameters which describe these phenomena have been investigated. The forms of the kinetic rate expressions for the catalytic reaction of adsorbed oxygen with hydrogen are different for ordered and disordered arrays of oxygen adatoms. In agreement with co-adsorption studies of hydrogen and oxygen, and supported by studies of hydrogen chemisorption on clean Rh(111), this implies that the rate of adsorption of hydrogen is sensitive to the structure of the adsorbed oxygen lattice.
\r\n\r\nTwo forms of molecularly adsorbed NO are readily distinguished on a Ru(001) surface by the frequencies of the nitrogen-oxygen stretching vibrations, which can then be used to observe the influence of co-adsorbates. Oxygen, nitrogen and hydrogen adatoms compete selectively for the adsites which are occupied by multiply-coordinated NO, whereas CO competes for adsites occupied by the singly-coordinated molecular NO. Carbon monoxide can even induce conversion of adsorbed molecular NO from sites of single coordination to sites of multiple coordination with the metal substrate.
\r\n\r\nWater interacts with the Ru(001) surface to form chemisorption bonds, but it also forms intermolecular hydrogen bonds which are of comparable strength. This leads to formation of layered, hydrogen bonded aggregates at all coverages. The properties of the first two layers are distinct from those of the subsequent ice multilayers, and a specific structural model for the hydrogen bonded lattices is proposed. A thermally induced ordering effect is observed which is analogous to the vitreous-to-cubic phase transformation of bulk ice.
", "doi": "10.7907/8m9w-p414", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:14369", "collection": "thesis", "collection_id": "14369", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09222021-222748217", "primary_object_url": { "basename": "Coggiola_MJ_1975.pdf", "content": "final", "filesize": 109080056, "license": "other", "mime_type": "application/pdf", "url": "/14369/1/Coggiola_MJ_1975.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Experimental Investigations of Molecule-Molecule and Electron-Molecule Scattering", "author": [ { "family_name": "Coggiola", "given_name": "Michael John", "clpid": "Coggiola-Michael-John" } ], "thesis_advisor": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Part I. Crossed molecular beam methods have been used to measure the differential elastic scattering of molecular hydrogen and deuterium with a number of diatomic and polyatomic secondary molecules. In particular, H2 + O2, SF6, NH3, H2O, CO and CH4 and D2 + O2, SF6, NH3, and H2O were all studied using thermal energy beams. The H2 + NH3 and H2 + SF6 systems were further studied using an H2 beam cooled to liquid nitrogen temperature. In addition, the H2 + SF6 system was remeasured using a beam of cooled para-hydrogen in place of the normal-hydrogen. These studies cover a wide range of anisotropy, size and initial relative collision energy of the scattering partners, as well as the corresponding de Broglie wavelengths. Each system studied yielded rapid quantum oscillations in the differential cross section which were used to determine central-field intermolecular potentials. These potentials were found to be independent of the energy and the hydrogen isotope used as well as their assumed mathematical form. As a result, the effects of anisotropy on the differential elastic scattering of these H2 and D2 systems do not seem important.
\r\n\r\nPart II. Variable angle electron impact spectroscopy has been applied to the systematic study of the electronic structure of the fluoroethylenes. Excitation spectra were obtained at 40 eV and 20 eV or 25 eV impact energies, and scattering angles from 0\u00b0 to 80\u00b0. Each of the molecules shows an absorption maximum between 4.2 eV and 4.7 eV, corresponding to the singlet \u2192 triplet, \u03c0 \u2192 \u03c0* transition similar to the N \u2192 T transition seen in ethylene. A weak absorption at 6.45 eV observed only in monofluoroethylene is assigned to the second singlet \u2192 triplet transition. Also observed in each spectrum is the strong singlet \u2192 singlet N \u2192 V transition, as well as a number of Rydberg features. Beyond the first ionization potential, a number of broad absorption features are observed in each molecule, corresponding to superexcited state transitions. Using a method based on term values, a number of these transitions have been assigned to Rydberg series converging to higher ionization potentials. The implications of these results for the photochemistry of the fluoroethylenes is also discussed.
\r\n\r\nChlorotrifluoroethylene has also been studied by the electron impact method, and the results are similar to those found for trifluoroethylene.
", "doi": "10.7907/r4tc-py47", "publication_date": "1975", "thesis_type": "phd", "thesis_year": "1975" }, { "id": "thesis:10768", "collection": "thesis", "collection_id": "10768", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03092018-170506721", "primary_object_url": { "basename": "Abel_RH_1971.pdf", "content": "final", "filesize": 34829886, "license": "other", "mime_type": "application/pdf", "url": "/10768/1/Abel_RH_1971.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Electrode Kinetic Studies Using a Computerized Data Acquisition and Analysis System", "author": [ { "family_name": "Abel", "given_name": "Roger Henry", "clpid": "Abel-Roger-Henry" } ], "thesis_advisor": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" } ], "thesis_committee": [ { "family_name": "Kuppermann", "given_name": "Aron", "clpid": "Kuppermann-A" }, { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Chan", "given_name": "Sunney I.", "clpid": "Chan-S-I" }, { "family_name": "Roberts", "given_name": "John D.", "clpid": "Roberts-J-D" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The first section of this dissertation introduces the basic concepts that are necessary for the quantitative description of electrode kinetics. The refinements and corrections in the rate equation that are due to a detailed model of the electrical double layer, and to the potential step relaxation technique are introduced and discussed.
\r\n\r\nA discussion of the non-linear statistical analysis techniques that are necessary for a rigorous analysis of rate equation is presented in the second section. The estimates of the precision of the desired parameters obtained by using statistical methods can be used as a measure of the efficiency of an experiment. Their use as measures of \"kinetic information density\" is developed and illustrated by comparing charge and current measurement in the potential step technique. Previous approaches to the subject of \"kinetic information density\" are discussed and compared to the results from statistical analysis.
\r\n\r\nThe third section describes the computerized data acquisition and analysis system that was designed and used for the study of electrode kinetics.
\r\n\r\nThe final section presents the results of the kinetic studies undertaken on the Zn+2/Zn(Hg) system in 1 F NaNO3, 1 F NaClO4, and 1 F NaCl supporting electrolytes. Ensemble averaging is used in these studies to increase precision and its values is illustrated.
\r\n\r\nThe results that are obtained for the rate constants in the various supporting electrolytes are compared and it is shown that the rates are comparable in NaNO3 and NaClO4 supporting electrolytes but significantly greater in 1 F NaCl. These results are compared with results of previous investigators and the quality of the results of this thesis are compared to those of previous investigators.
", "doi": "10.7907/HT2Z-3059", "publication_date": "1971", "thesis_type": "phd", "thesis_year": "1971" } ]