This thesis presents work on the heterogeneous chemistry of surfactant monolayers adsorbed at the air-water interface with gas phase hydroxyl radicals (OH). A novel hydroxyl radical source utilizing a low-temperature plasma known as the dielectric barrier discharge source (DBDS) is designed, characterized, and implemented as a high concentration OH generator (approximately 1000 fold higher than ambient conditions) in these experiments. Millimeter-sized water droplets containing a monolayer of surface-adsorbed species are exposed to this OH source until a designated level of oxidation. Field-induced droplet ionization mass spectrometry (FIDI-MS), which has been previously proven to be a surface-selective ionization technique, is used as an analytical method to determine the identity and relative quantity of oxidation products at the interface by sampling progeny droplets expelled upon the application of a pulsed electric field. Chapter 2 establishes the utility of the DBDS and FIDI-MS setup by oxidizing the 12-carbon n-alkyl surfactant dodecyltrimethylammonium (DTA+). Mechanistic details can be determined through the evolution of high mass oxidation products through a nearly complete conversion of the parent monolayer. Carbonyl, hydroxyl, peroxyl, and small amounts of fragmentation products can be discerned from the collision-induced dissociation mass spectra and through hydrogen-deuterium exchange experiments. Psuedo-first order kinetics can also be observed in this system, suggesting a Langmuir-Hinshelwood mechanism of OH-initiated oxidation. Chapter 3 extends the study of oxidation of hydrocarbon surfactants by looking at neighbor chain competition among a bis-quaternary ammonium gemini surfactants, a species that contains two long alkyl chains. Specifically, the experiment assesses the ability of two non-identical alkyl chains to compete with each other for the impinging gas phase hydroxyl radical. The increased reactivity of singly oxidized chains is evaluated by the oxidation of a gemini surfactant parent with identical alkyl chains. Chapter 4 investigates the oxidation of α,ω-surfactants, those that contain polar functional group separated by methylene spacers, discussing deviations of this class of surfactants with those that contain only one head group (i.e. DTA+). Chapter 5 demonstrates the DBDS and FIDI-MS system for use as a peptide footprinting technique for the amphiphilic species substance P. Localization of the site of oxidation can be done through FIDI-MS/MS analysis.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/Z9SN06XG, author = {Thomas, Daniel Aaron}, title = {Chemical Reaction Dynamics of the Liquid/Vapor Interface Studied by Mass Spectrometry}, school = {California Institute of Technology}, year = {2016}, doi = {10.7907/Z9SN06XG}, url = {https://resolver.caltech.edu/CaltechTHESIS:05182016-140524270}, abstract = {This thesis presents investigations of chemical reactions occurring at the liquid/vapor interface studied using novel sampling methodologies coupled with detection by mass spectrometry. Chapters 2 and 3 utilize the recently developed technique of field-induced droplet ionization mass spectrometry (FIDI-MS), in which the application of a strong electric field to a pendant microliter droplet results in the ejection of highly charged progeny droplets from the liquid surface. In Chapter 2, this method is employed to study the base-catalyzed dissociation of a surfactant molecule at the liquid/vapor interface upon uptake of ammonia from the gas phase. This process is observed to occur without significant modulation of the bulk solution pH, suggesting a transient increase in surface pH following the uptake of gaseous ammonia. Chapter 3 presents real-time studies of the oxidation of the model tropospheric organic compound glycolaldehyde by photodissociation of iron (III) oxalate complexes. The oxidation products of glycolaldehyde formed in this process are identified, and experiments in a deoxygenated environment identify the role of oxygen in the oxidation pathway and in the regeneration of iron (III) following photo-initiated reduction. Chapter 4 explores alternative methods for the study of heterogeneous reaction processes by mass spectrometric sampling from liquid surfaces. Bursting bubble ionization (BBI) and interfacial sampling with an acoustic transducer (ISAT) generate nanoliter droplets from a liquid surface that can be sampled via the atmospheric pressure interface of a mass spectrometer. Experiments on the oxidation of oleic acid by ozone using ISAT are also presented. Chapters 5 and 6 detail mechanistic studies and applications of free-radical-initiated peptide sequencing (FRIPS), a technique employing gas-phase free radical chemistry to the sequencing of peptides and proteins by mass spectrometry. Chapter 5 presents experimental and theoretical studies on the anomalous mechanism of dissociation observed in the presence of serine and threonine residues in peptides. Chapter 6 demonstrates the combination of FRIPS with ion mobility-mass spectrometry (IM-MS) for the separation of isomeric peptides.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/HRF2-FJ21, author = {Sohn, Chang Ho}, title = {New Reagents and Methods for Mass Spectrometry-based Proteomics Investigations}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/HRF2-FJ21}, url = {https://resolver.caltech.edu/CaltechTHESIS:02162011-180032183}, abstract = {New chemical reagents and methods have been employed for mass spectrometry (MS)-based proteomics investigations. Many chemical reagents are synthesized to be covalently attached to biomolecules, especially peptides and proteins. The properties of the resulting peptide conjugates are characterized by various tandem mass spectrometric techniques (e.g., collision-induced dissociation (CID), electron capture dissociation (ECD), electron transfer dissociation (ETD), infrared multiphoton dissociation (IRMPD), and free radical initiated peptide sequencing (FRIPS)). In Chapter 2, the effect of high electron affinity tags in ECD and ETD is investigated using their peptide conjugates. The initial intramolecular electron transfer from the high-lying Rydberg states to the covalently attached high electron affinity tag occurs in competition with the Coulomb stabilized π* orbitals of the amide bonds in the model peptides. This leads to the inhibition of the normal sequence of ECD and ETD processes, yielding no backbone fragmentations. In Chapter 3, selective disulfide bond cleavages are observed by the FRIPS method. A newly prepared TEMPO-based FRIPS reagent is labeled to model peptides containing disulfide bonds and subject to CID to monitor free radical induced cleavages. Highly selective C–S and S–S bond cleavages are observed and their reaction mechanisms are proposed. In Chapter 4, novel Caltech isobaric tags (CITs) for protein quantification are developed and validated using various model samples. A newly discovered low-energy gas-phase fragmentation pathway, a nucleophilic substitution of the N3 in the 1,2,3-triazole ring generated by copper-catalyzed azide-alkyne cycloaddition (CuAAC) inspired us to create CITs. This selective cleavage is applied to the formation of the reporter ions to quantify protein expression level in cells. Chapter 5 describes clickable cross-linkers (CXLs) developed for elucidation of three-dimensional protein structures and protein-protein interactions (PPIs). In CXLs, cross-linking reactions are separated from the conjugation of affinity tags, avoiding steric hindrance. Cross-linked peptides are enriched from the complex mixture of yeast lysate and cross-linked ubiquitin digests using avidin affinity chromatography, showing high sensitivity of the CXL-based analysis. The low-energy pathway used for CIT reagents is also adopted to produce the reporter ion, filtering MS/MS scans of cross-linked peptides from those of unmodified peptides.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/M86B-8T98, author = {Neidholdt, Evan Lyle}, title = {Novel Pyroelectric and Switched Ferroelectric Ion Sources in Mass Spectrometry: Implementation and Applications}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/M86B-8T98}, url = {https://resolver.caltech.edu/CaltechTHESIS:03292010-222225209}, abstract = {Instrumentation development for ambient mass spectrometry is an ever-changing and ever-growing field, often emphasizing the development of field-portable, ruggedized instrumentation. This thesis presents work in the area of ion source development. Specifically, two novel ionizers for mass spectrometry are constructed, implemented, and tested on a variety of systems. The first, the ambient pressure pyroelectric ion source (APPIS) comprises a z-cut lithium niobate or lithium tantalate pyroelectric crystal which is subjected to thermal cycling. Thermal cycling and the pyroelectric effect result in the buildup of excess charge on the z-faces of the material. For a temperature change of only 30 K, an electrical potential as high as 70,000 V could be built up if no discharging occurs. At ambient pressure, electrical discharges occur between the oppositely charged crystal faces and regions of different potentials on the same crystal face. Monitoring of the discharges using an inductive pickup reveals that the time frame of ion production corresponds to that of electrical activity on the crystal face. Additionally, the ions observed in the mass spectra differ when different ambient gas compositions are present. This, and comparison to APCI experiments reveals that ionization with APPIS is a gas phase process and observed product ion species are highly dependent on ambient gas composition. An application of APPIS, whereby APPIS is used as an ion source for the detection of chemical warfare agents, is presented. Agents in the V and G classes possess amine functionality, and as a result have relatively high proton affinities and are well suited to ionization and detection using chemical ionization with APPIS. Simulants for the nerve agents VX and Tabun were detected as singly protonated species using APPIS.
A second ion source for ambient mass spectrometry is also presented, the switched ferroelectric plasma ionizer (SwiFerr). The source comprises a 1 mm thick plate of barium titanate with an electrode on one face and a grounded metallic grid on the opposite face. If an audio frequency high voltage waveform is applied to the electrode, domain structure is formed and the high electric fields across domain walls give rise to electron emission and plasma formation. At ambient pressure, the plasma produces chemical ionization reagent ions which participate in proton transfer reactions with trace species in ambient air. The source is useful for examining organic vapors and solid samples. Solid sampling is achieved through use of a pneumatic aspirator, which can aspirate powders into the SwiFerr source for analysis. Powders of the drugs loperamide and ibuprofen were ionized and detected using SwiFerr. A second-generation SwiFerr source has been designed and implemented, and is described. The second-generation source is constructed in a unibody fashion, such that the rear electrode, grid, and electrical contact wires are attached as a single unit using conductive adhesives. This allows for a source which is further miniaturized and capable of insertion into a standard Swagelok fitting, for ease of integration into existing instrumentation. The source is particularly sensitive, and an application involving detection of trace explosives is presented. Nanogram quantity samples of TNT were ionized and detected with SwiFerr after volatilization using a rudimentary thermal desorption apparatus. Sensitive detection of TNT suggests use of SwiFerr in applications where sensitive detection in field portable instrumentation is desired. To this end, plans for a stand-alone power supply for this ionizer as well as a supply designed for operating the source in a constant discharge mode at low power are presented in an appendix.
Additional work not related to ion source development is also presented in this thesis. Chapter 6 presents advances in free radical initiated peptide sequencing (FRIPS). The 20 amino acid basis set has been analyzed for reactivity with acetyl radical, and distinct reactivity classes are observed. Chapter 7 presents a study of regioselective cleavage at aspartic acid residues by various cations. Selective cleavage at aspartic acid is observed for any cation which is not mobile along the peptide backbone, and fragmentation proceeds through a salt bridge mechanism.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/QQFG-WG57, author = {Kim, Hugh Inkon}, title = {Fundamental and Applied Studies of the Structures and Reaction Dynamics of Biomolecules Using Mass Spectrometry and Ion Mobility Spectrometry}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/QQFG-WG57}, url = {https://resolver.caltech.edu/CaltechETD:etd-05092008-165701}, abstract = {Chapter 1 reviews studies of non-covalently bound metal complexes related to the structures and reactions of biomolecules in the gas phase, chapter 2 introduces the Route 66 method for identifying disulfide linkages in peptides using mass spectrometry. Collisional activation of singly charged cationic alkali and alkaline earth metal complexes of peptides with disulfide linkages results in highly selective elimination of hydrogen disulfide (H₂S₂). Further activation of the product yields amino acid sequence information in the region previously short-circuited by the disulfide bond. In chapter 3, we demonstrate applications of this methodology by identifying three disulfide linkages in insulin with a peptic digest using the Route 66 method. In chapters 4 and 5, gas phase reactions triggered by the bimolecular collision of a water molecule with collisionally activated anionic and cationic sodiated dicarboxylic acid clusters are examined. The water molecule serves as a proton donor for a dicarboxylate anion in the cluster and introduces energetically favorable dissociation pathways, such as the decomposition of the malonate ion, to yield an acetate ion and CO₂.
To further explore the utility of IMS in the identification of organic compounds on other planetary bodies, pursuant to NASA objectives, ion mobilities are investigated for different classes of biomolecules. Chapters 6 and 7 report the reduced ion mobilities of protonated amino acid cations and deprotoanted carboxylate anions, respectively, determined in both N₂ and CO₂ drift gases. A 12-4 potential model for the ion-neutral interaction is used to investigate the high correlation observed between masses and mobilities of the ions. Computational analysis employing a 12-4 model supports ring conformations for multicarboxylate anions consistent with higher ion mobility values than calculated for extended structures. In Chapter 8, the ion mobilities of tertiary and quaternary ammonium cations in N₂ are reported along with their high mass-mobility correlation. We also detail the sensitivity of the collision cross sections of molecular ions to the ion-neutral interactions using the classical ion-neutral collision model and the computational trajectory method. The shape asymmetry of the ammonium cations plays an important role in determining the observed correlation between mass and mobility.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/E8EV-W425, author = {Grimm, Ronald L.}, title = {Fundamental Studies of the Mechanisms and Applications of Field-Induced Droplet Ionization Mass Spectrometry and Electrospray Mass Spectrometry}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/E8EV-W425}, url = {https://resolver.caltech.edu/CaltechETD:etd-10092005-222651}, abstract = {This thesis explores the evaporation and Rayleigh discharge dynamics of highly charged micron-sized droplets and explores new methodologies for extracting ions for mass analysis from neutral droplets using strong electric fields in a technique termed field-induced droplet ionization.
A phase Doppler anemometer characterizes individual highly charged droplets moving through a uniform, mild electric field within an ion mobility cell according to size, velocity, and charge. Repeated reversals of the electric field allow multiple characterizations on selected droplets. This “ping-pong” technique provides droplet histories that determine the solvent evaporation and Rayleigh discharge behavior. The ping-pong experiment characterizes volatile droplets of the hydrocarbon solvents n-heptane, n-octane, and p-xylene as well as two-component droplets of either 2-methoxyethanol, tert-butanol, or m-nitrobenzyl alcohol with methanol. On average, hydrocarbon droplets eject 18% of their net charge into progeny droplets with an undetectable loss in mass. Rayleigh discharge events in the polar, binary droplets release between 20 and 35% of the net charge with a correspondingly undetectable loss in mass.
In other experiments, strong electric fields elongate neutral droplets along the field axis. Field-induced droplet ionization (FIDI) occurs at sufficient field strengths as the droplets eject opposing jets of positively and negatively charged progeny droplets. Images of droplets from a vibrating orifice aerosol generator illustrate this phenomenon, and mass spectrometric sampling of the progeny droplets demonstrates that they are a viable source of desolvated gas-phase ions. Switched electric field experiments relate the timescale of droplet elongation and progeny droplet formation in FIDI to the timescale of oscillations of droplets in sub-critical field strengths. FIDI mass spectra are presented for several species, including tetraheptyl ammonium cation, deprotonated benzene tetracarboxylic acid, and multiply protonated cytochrome c.
Droplets may serve as reactors before being sampled by FIDI-MS. FIDI-MS probes the products of heterogeneous reactions between solution-phase oleic acid or a lysophosphatidic acid and gas-phase ozone.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/NRTF-GH89, author = {Hodyss, Robert P.}, title = {Methods for the Analysis of Organic Chemistry on Titan}, school = {California Institute of Technology}, year = {2006}, doi = {10.7907/NRTF-GH89}, url = {https://resolver.caltech.edu/CaltechETD:etd-01122006-105657}, abstract = {Tholins are brownish, sticky residues formed by the energetic processing of mixtures of gases abundant in the cosmos, such as CH4, N2, and H2O, either with ultraviolet light or electrical discharge. This thesis describes investigations of the tholins produced by the processing of mixtures of N2 and CH4, as a model of photochemical processes occurring in the atmosphere of Titan. These compounds are mixed with liquid water during impacts or cryovolcanism, in melt pools which eventually freeze. The melt pools are interesting sites for astrobiological research, containing a wealth of organic material interacting over long time periods in a liquid water solvent. Studies of the near infrared reflectance spectrum and the fluorescent properties of the tholins are presented, yielding information on the composition of the tholins and a means of finding organic deposits on the surface of Titan. Tholin decomposition on heating is extensively investigated, partly to ascertain the utility of pyrolysis as a technique for tholin characterization. Tholins are found to undergo significant chemical change at temperatures as low as 100 °C, releasing large quantities of ammonia, while at higher temperatures, cyclizing and aromatizing reactions occur. Pyrolysis is thus not a good technique for the characterization of tholins. The development of two instruments for tholin characterization are also discussed: a gas chromatograph with an ultraviolet absorption detector, for functional group analysis of the tholins, and sensors designed for the determination of enantiomeric excess.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/AVWS-B055, author = {Sumner, Heather Ann}, title = {Gas Phase Reaction Dynamics and Design of Molecular Clusters and Bioconjugates}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/AVWS-B055}, url = {https://resolver.caltech.edu/CaltechETD:etd-05242005-144900}, abstract = {Chapter 1 serves as an introduction to the design of molecular clusters and bioconjugates that exhibit interesting reactivity in the gas phase. In Chapter 2, gas-phase reactions of clusters of alkylammonium ions with triphosphate, DNA, and peptides are examined. Alkylation of both phosphate and carboxylate groups is observed. In Chapter 3, the gas phase reactions of methyl phosphate noncovalently bound clusters are studied in detail. The presence of sodium ions in methyl phosphate clusters stabilizes the clusters, facilitating intermolecular condensation reactions between methyl phosphates.
In Chapter 4, the first gas-phase phosphorylation of molecules containing hydroxyl substituents is reported. Gas-phase reactions of triphosphate with hydroxyl-containing molecules result in phosphorylation of the hydroxyl substituent. In the absence of a hydroxyl substituent, the C-terminus of a peptide can be phosphorylated. Otherwise, hydroxyl residues are selectively phosphorylated.
Chapter 5 considers the possibility of free radical initiated peptide sequencing, or FRIPS, in the gas phase. A free radical initiator is conjugated to the N-terminus of peptides or proteins, forming a bioconjugate. Collision-induced dissociation of the conjugated species results in free radical formation. The free radical then fragments on further collisional activation to yield backbone fragmentation products. This technique may allow selective cleavage of peptides at specific amino acid residues, with applications to gas-phase proteomics sequencing efforts.
Chapters 6 deals with experiments conducted on solvated ions, specifically focusing on the evaporation kinetics and the relative intensities of differently solvated species. Water cluster distributions are used to discriminate between isomers and enantiomers. Chapter 6 also includes data on the reaction of t-butyl chloride in water clusters, as well as data on doubly charged cationic species showing pairwise evaporation of water.
Chapter 7 uses H/D exchange experiments to examine the behavior of sodiated glycine oligomers, ranging from Gly1 to Gly5. It is found that H/D exchange dynamics do not directly reflect the structure of sodiated glycine oligomers, as the solvation energy provided by the exchange reagent can allow the ion-molecule complex to access high-energy states. Therefore, interpretations of H/D exchange results should be conducted with detailed examinations of possible exchange mechanisms.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/2E8R-G492, author = {Austin, Daniel Ephraim}, title = {Impact-Ionization Mass Spectrometry of Cosmic Dust}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/2E8R-G492}, url = {https://resolver.caltech.edu/CaltechETD:etd-11072002-135150}, abstract = {In situ characterization of cosmic dust grains typically involves impact-ionization time-of-flight mass spectrometry. Considering the performance and limitations of previous instruments, I designed and tested a novel, compact time-of-flight mass spectrometer for cosmic dust analysis. The instrument, Dustbuster, incorporates a large target area with a reflectron, simultaneously optimizing mass resolution, particle detection, and ion collection. Dust particles hit the 65-cm² target plate and are partially ionized by the impact. The resulting ions, with broad energy and angular distributions, are accelerated through the modified reflectron, focusing ions spatially and temporally to produce high-resolution spectra.
Initial performance tests of the Dustbuster used laser desorption ionization of embedded metal and mineral samples to simulate particle impacts. Mass resolution (mass/peakwidth) in these experiments ranged from 60 to 180, permitting resolution of isotopes. Subsequent experiments included hypervelocity microparticle impacts. Charged iron and copper microparticles, accelerated to 2-20 km/s in a 2 MV van de Graaff accelerator, impacted the Dustbuster. Mass resolution in these experiments ranged from 150 to 300 for iron and copper. Hydrogen, carbon, and oxygen ions appeared in many spectra. Field-induced emission of electrons immediately before impact is a possible cause of ion formation from species with high ionization potentials. The implications of this ionization effect are discussed in relation to interpretation of mass spectra from other in situ dust analyzers.
Another time-of-flight instrument, originally designed as an energy analyzer, shows promise as a high-resolution mass spectrometer for high-flux cosmic dust environments.
Ice is an important component of particulates ejected from comets and other icy bodies in the solar system. Due to limited experimental data on ice particle impacts, I built an ice particle source based on a vibrating orifice aerosol generator connected directly to vacuum. Ice particles produced in this manner can be electrostatically accelerated for impact ionization studies.
Hypervelocity impact vaporization may have played a key role in the mass extinction that occurred at the Cretaceous-Tertiary (K-T) boundary. In order to study the speciation of gases that may have been produced in such an asteroid impact, I designed a specialized orthogonal extraction mass spectrometer for future laboratory impact experiments.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, } @phdthesis{10.7907/8D4X-RE68, author = {Julian, Ryan Roy}, title = {Molecular Recognition of Biomolecules in the Gas Phase}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/8D4X-RE68}, url = {https://resolver.caltech.edu/CaltechETD:etd-04292003-134947}, abstract = {The first chapter introduces the most relevant noncovalent forces for gas phase experiments. Chapters 2-5 contain work on small clusters of biologically relevant molecules. In Chapter 2, it is shown that the unusual properties of arginine lead to extensive noncovalent clustering of this amino acid, when sampled by ESI-MS. The stability of the zwitterionic form of arginine for clusters without a net charge is addressed by theoretical methods in Chapter 3.
In Chapter 4, the properties of the unusually abundant serine octamer are examined. Experiments demonstrate that this octamer has a strong preference to be homochiral. A structure for the serine octamer is proposed that is cubic and has a zwitterionic core. The results gathered from the serine octamer demonstrate that a homochiral preference can exist for very small clusters or “nanocrystals.”
The first gas phase synthesis for ATP is given in Chapter 5. ATP is easily synthesized in the gas phase from a cluster of three AMP molecules bound by a sodium salt bridge. Subsequent CAD spectra following the gas phase synthesis are identical to those obtained from an authentic sample of ATP in separate experiments.
Chapters 7-9 deal with the molecular recognition of amino acid side chains in ESI-MS experiments. The ability of 18C6 to recognize and selectively attach to lysine residues is explored. Recognition of arginine side chains is accomplished in a similar manner by utilizing the larger dibenzo-30-crown-10 ether (DB30C10). The two techniques are mutually compatible, allowing for both crowns to be added to the same solution.
Chapters 10-11 combine the recognition of 18C6 with various chemical functionalities in order to mediate peptide chemistry in the gas phase. In Chapter 10, a new class of molecules termed ?molecular mousetraps? is described. The mousetraps combine the recognition of 18C6 with the chemical reactivity of diazo groups. The resulting molecules are capable of noncovalently attaching to any molecule that contains a protonated primary amine. CAD can be utilized to activate the complex. In Chapter 11, the mousetraps are utilized in experiments with peptides. It is shown that covalent attachment can be achieved in a quantitative fashion.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/M9MM-6Z40, author = {Smith, James N.}, title = {A. Computational chemistry applied to the analysis of air pollution reaction mechanisms ; B. Fundamental studies of droplet evaporation and discharge dynamics in electrospray ionization}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/M9MM-6Z40}, url = {https://resolver.caltech.edu/CaltechETD:etd-09202007-080810}, abstract = {The first part of the thesis investigates the use of theoretical quantum chemical calculations for the study of the reaction pathways of the atmospheric aromatic-OH reaction. The computational model is comprised of a semi-empirical PM3 geometry optimization followed by a single point calculation performed using the Becke3LYP hybrid density functional and a 6-31G(d,p) basis. Zero-point energies were calculated using PM3, and transition states barrier heights estimated by a constrained optimization procedure developed for this study. Full mechanisms for the OH-initiated photooxidation of toluene, m-xylene, p-xylene, 1,2,4-trimethylbenzene and m-ethyltoluene are developed. The lowest energy intermediates have been determined and predicted products from these structures are compared to available experimental product data. These studies serve to refine proposed mechanisms currently available for toluene, mxylene and p-xylene, while providing new information on the 1,2,4-trimethylbenzene and m-ethyltoluene reaction pathways. In the second part of the thesis, an experimental technique is described for probing the mechanism and dynamics of charged droplet breakup in electrospray ionization. At its core is an instrument that can perform simultaneous, in situ measurements of size and charge on individual droplets. Charged droplets are sampled directly from the spray source into a drift cell with a uniform electric field. A simultaneous diameter and charge measurement is made on individual droplets at the center of the cell using phase Doppler anemometry. By reversing the field in the drift chamber once the initial size and charge measurement is made, the droplet can be made to pass again through the measurement region of the phase Doppler anemometer. In this way, repeated measurements of the size and charge can be made on a single droplet. This technique has been applied to a variety of solutions used commonly in electrospray ionization and lead to the following generalizations. (1) The discharge dynamics of droplets with the same initial diameter and charge are highly reproducible for all solvents and analyte/solvent combinations studied to date. (2) Published over a hundred years ago, Lord Rayleigh’s analysis of charged droplet instabilities resulting from solvent evaporation is remarkably accurate in predicting observed discharge events for all three solvents. (3) Droplet discharge events are characterized by loss of 15-20% of the charge from methanol and acetonitrile droplets, and 20-40% from water droplets, with little accompanying loss of solvent. (4) Discharge events occur in a reproducible temporal pattern, with decreasing time intervals between successive events, dictated by solvent evaporation and the approach to the Rayleigh limit. The droplet size decrease agrees well with a model of solvent evaporation. (5) The addition of biomolecules or salt (up to 10[superscript -3] M to the solution does not significantly alter discharge dynamics. The size-charge correlation and discharge dynamics of negatively charged droplets formed in electrospray ionization of 10[superscript -4] M NaCl in methanol are similar to those observed for positively charged droplets. (6) The life history of a single electrosprayed droplet can be followed through numerous discharge events (sequences with up to 50 measurements and 6 discharges have been observed) in the absence of radial confinement. This implies that no significant displacement of the droplet arises from discharge events and is inconsistent with any notion of high energy chaotic fission processes. (7) Droplet size-charge correlations show that, in certain instances, droplets from an electrospray fall into discrete groupings that can be attributed to fission events.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Flagan, Richard C. and Beauchamp, Jesse L.}, } @phdthesis{10.7907/at5p-pe62, author = {Kossakovski, Dmitri A.}, title = {Scanning probe chemical and topographical microanalysis}, school = {California Institute of Technology}, year = {2000}, doi = {10.7907/at5p-pe62}, url = {https://resolver.caltech.edu/CaltechETD:etd-02272009-085501}, abstract = {The last decade has seen a rapid rise of Scanning Probe Microscopy, SPM, as a prominent and versatile approach for surface studies. SPM instruments are differentiated from the beam-based ones by the fact that they use solid proximal probes for localized analysis. The most commonly used SPM methodology is Atomic Force Microscopy, AFM. In its basic implementation, AFM provides topographical information with nanometer resolution. The most common modifications allow the magnetic, electrostatic, and specific chemical environment to be examined. However, there is no direct way today to perform general chemical analysis with AFM probes.
Near-field Scanning Optical Microscopy, NSOM, is another variation of SPM where sharp tapered optical fibers serve dual purposes, being proximal probes of sample topography, and providing the means for localized light delivery for optical studies with sub-wavelength spatial resolution. Again, NSOM itself does not have a general chemical contrast capability. However, the capability to deliver light to localized area opens the way to a multitude of experiments that can be devised using different aspects of light interaction with the sample.
This thesis demonstrates several approaches for combined topographical and chemical investigations. Infrared spectroscopy is a sensitive molecular analysis tool. Without scanning proximal probe, IR microscopy has very poor spatial resolution. Enabling methodology for probe fabrication for Near-field Scanning Infrared Microscopy, NSIM, is presented.
The efforts in combining NSOM with mass spectrometry, which is probably the most general chemical analysis tool, are outlined. We have demonstrated the possibility of simultaneous topographical and molecular imaging.
Another variation of chemical imaging is the combination of SPM and Laser Induced Breakdown Spectroscopy, LIBS. In this method the elemental composition of samples is obtained by analyzing optical emissions from transient plasma plumes formed by intense laser pulses delivered through fiber probes. We have demonstrated the feasibility of this approach. The instrument that we have developed is an attractive complementary tool for established methods of spatial elemental analysis, such as X-ray Fluorescence. Among its attractive features are operation in ambient conditions, minimal requirements for sample preparation, and ease of use.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/8gqa-0x72, author = {Lee, Hak-No}, title = {I. Gas Phase Proton Affinity of Zwitterionic Betaine. II. High Resolution Spectroscopy of Trapped Ions: Concept and Design}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/8gqa-0x72}, url = {https://resolver.caltech.edu/CaltechTHESIS:11212019-155237296}, abstract = {In an ideal experiment, the system being investigated is isolated from the environment. The only external influences allowed on the system are the parameters that the experimenter chooses to vary, in effort to study their effects on the observables. Moreover, these parameters can be controlled with all the accuracy and precision desired by the experimenter. In chemistry, ion cyclotron resonance (ICR) mass spectrometry may come closer to replicating this ideal condition than any other experimental technique. An ion isolated in an ICR trap is under ultra high vacuum, devoid of physical contact with other atomic and molecular systems, as well as with the apparatus itself. Confined to a small volume and for a practically unlimited length of time, its few connections with the external environment, such as temperature and the electric and magnetic trapping fields, are well under the experimenter’s control. And since the motion of a charged particle in electric and magnetic fields is completely known, the ion can be manipulated with an unequaled freedom and certainty. In this dissertation, two experimental methods which utilize these unique capabilities of ICR spectrometry are explored.
In Chapter 1, the kinetic method is applied to determine the gas phase proton affinity of the zwitterion betaine, (CH₃)₃N⁺CH₂CO₂⁻. Protonated dimers of betaine with reference bases of known proton affinities are formed by Cs⁺ bombardment of a glycerol solution in an external ion source FT-ICR. Product distributions resulting from off-resonance collisional activation of isolated adducts are analyzed to yield a value of 242 ± 1 kcal/mol for the gas phase proton affinity of betaine. This is 103 kcal/mol less than that of the isoelectronic tert-butylacetate anion, (CH₃)₃CCH₂CO₂⁻, and the difference can be attributed to the electrostatic dipolar stabilization of the carboxylate anion in betaine. In addition, a general analysis of the kinetic method is presented based on RRKM unimolecular reaction theory. This analysis does not assume a Boltzmann distribution of internal energies in the reactant ion and provides a rationalization for the success of the method even when different experimental techniques are used.
While ICR has proven to be a powerful technique for studying the chemical properties of gas phase ions, it suffers from a serious weakness which prevents full realization of its unique capabilties: The only observable it measures is the mass. This has kept ICR from being widely used to investigate the physical properties of molecular ions. In Chapter 2, a novel method for obtaining high-resolution r.f. and microwave spectra of ions in ICR trap is proposed. Termed internally resonant ion trapping excitation (IRITE), it uses spatially inhomogeneous a.c. electric fields to couple the internal energy states with the ion’s translation motion. The resonance absorption of radiation is detected by its effect on the oscillations of the trapped ions, rather than on the radiation. The theoretical concept behind IRITE is introduced, and an experiment designed to demonstrate its feasibility by observing r.f. transitions in HCl⁺ is discussed in details. Combined with ICR’s unsurpassed ability to isolate and manipulate chemical systems, this new technique promises to allow chemists to study phenomena previously unobservable even in neutral molecules.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/p8bs-x927, author = {Crellin, Kevin Christopher}, title = {The investigation of gas-phase ion-molecule reactions with fourier transform ion cyclotron resonance mass spectrometry}, school = {California Institute of Technology}, year = {1997}, doi = {10.7907/p8bs-x927}, url = {https://resolver.caltech.edu/CaltechTHESIS:10222009-123129177}, abstract = {The gas-phase chemistry of several chemical systems have been investigated with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The emphasis of these experiments is on organoscandium ion chemistry, but inorganic and organic systems have also been examined. Furthermore, quantum mechanical calculations have been performed on selected systems to help in the interpretation of the experimental data or guide the experiments. Chapter 1 is a brief review of the experimental aspects of FT-ICR mass spectrometry. The history of the development of FT-ICR is given, and the instrumentation required to perform FT-ICR mass spectrometry is described. The mathematical description of ion motion is discussed, and applied to the description of the excitation and detection of ions. A short explanation of how these aspects are combined to form a standard experimental event sequence is then presented. Chapters 2-5 present the results of our investigations of the reactivity of organoscandium ions with alkanes and alcohols. In Chapter 2 we examine the reactions of Sc(CH_3)_2^+ with methane, ethane, [2,2-D_2]-propane, [1,1,1,4,4,4-D_6]-n-butane and [2- D]-isobutane, while in Chapter 3 the reactions of CH_3ScCH_2CH_3^+ with methane, ethane, [2,2-D_2]-propane, [1,1,1,4,4,4-D_6]-n-butane, [2-D]-isobutane and n-pentane are observed. In both systems σ-bond metathesis reactions similar to those observed in liquid-phase systems are seen. Site selectivity with the larger alkanes is also observed with the aid of deuterium labeling. In Chapter 4 we return to the Sc(CH_3)_2^+ ion and investigate its reactivity with cyclopentane and cyclohexane. Once again, σ-bond metathesis reactions are observed, this time with secondary C-H bonds rather than primary C-H bonds (as seen with the straight- and branched-chain hydrocarbons). We then change our focus in Chapter 5 to the σ-bond metathesis reactions of Sc(OCD_3)_2^+ with water, ethanol and 1-propanol. Again, σ-bond metathesis reactions were seen. However, in this case ligand exchange equilibria were observed via σ-bond metathesis and used to evaluate the relative bond energies of various Sc^+ alkoxide bonds. Chapters 6-8 move away from organoscandium systems and into various inorganic and organic systems. In chapter 6 the reaction of Cl^- with C1ONO_2 is examined. This reaction was found to be fast and efficient in the gas phase, which raises the possibility that Cl^- might react directly with C1ONO_2 on water ice films on the surface of type II polar stratospheric cloud particles. Chapter 7 investigates the reactions of nitrobenzene and the explosives 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5- triazacyclohexane (RDX) with Si(CH_3)_3^+. Adduct formation and small amounts of characteristic fragmentation (with the TNT and RDX adducts) is observed, suggesting that these types of reactions could be useful as a detection scheme for common explosives. Chapter 8 extends this work to the explosives EGDN (ethylene glycol dinitrate) and PETN (pentaerythritol tetranitrate). These nitrate ester explosives do react with Si(CH_3)_3^+, but no molecular adduct is seen in the FT-ICR mass spectrometer. However, characteristic fragment ions are seen and the PETN-Si(CH_3)_3^+ adduct can be seen in a sector mass spectrometer. The differences in the reactivity of nitro explosives and nitrate ester explosives are also discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/z6t6-nz51, author = {Campbell, Sherrie A.}, title = {FT-ICR studies of the structures, energetics and reaction dynamics of biological molecules in the gas phase}, school = {California Institute of Technology}, year = {1995}, doi = {10.7907/z6t6-nz51}, url = {https://resolver.caltech.edu/CaltechETD:etd-05122005-160230}, abstract = {Fourier transform ion cyclotron resonance (FT-ICR) mass spectroscopy has been used to investigate the energetics and reaction dynamics of biological molecules in the gas phase. Experimental results aid in predicting gas phase protonation sites and molecular conformations of peptides and amino acids. Correlations of proton affinities with adiabatic lone-pair ionization energies indicate that amino acids lacking basic side chains protonate on the amine nitrogen, while more basic amino acids protonate on their side chain. These results have been similarly applied to small peptides, with protonation predicted on the N-terminus for peptides lacking basic amino acid residues.
Two novel experimental methods have been developed for measuring gas phase proton affinities, which utilize infrared multiphoton dissociation and collision induced dissociation techniques to cleave proton-bound dimers of reagent gases. The dimers fragment into two products with the more basic reagent retaining the proton. A simplified RRKM analysis is used to determine proton affinities from product ion abundances.
Isotopic hydrogen exchange reactions of protonated glycine oligomers with a series of reagent bases have been performed, and the exchange mechanisms and energetics identified. Although it is not the sole determining factor, the extent and rates of H/D exchange increase with reagent basicity, with ND3 being the most efficient exchange gas studied. Exchange of the N-terminus hydrogens occurs via an onium ion mechanism in which an endothermic proton transfer is rendered energetically favorable by simultaneous solvation of the ammonium ion. Exchange of the C-terminus occurs via a salt bridge intermediate, in which the carboxylate and ammonium ion is stabilized by interactions with the nearby protonated N-terminus.
Finally, the H/D exchange reactions of several peptides possessing basic residues with ND3 have been investigated. The results indicate that basic amino acids hinder exchange processes as protonation energetics and molecular folding become more important. Calculations using semiempirical AM1 and PM3 methods were performed to identify the gas phase configurations of the protonated peptides and determine if stable salt bridge structures are possible. Potential energy surfaces were also calculated for all exchange processes.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/ecqj-my65, author = {Marzluff, Elaine M.}, title = {Fundamental studies of the structures, energetics and collision dynamics of large molecules in the gas phase}, school = {California Institute of Technology}, year = {1995}, doi = {10.7907/ecqj-my65}, url = {https://resolver.caltech.edu/CaltechETD:etd-10172007-112712}, abstract = {The construction and application of an external source Fourier transform ion cyclotron resonance mass spectrometer equipped with a fast atom bombardment source for studies of biological molecules is described. The instrument features an octopole ion guide, Shulz-Phelps ionization gauge and 7-Tesla superconducting magnet and has been specifically designed for quantitative studies of biological molecules. The primary focus of the work described here has been the development of chemical and physical probes to examine the properties and structures of biomolecules in the gas phase.
The results of a complete study of the low energy dissociation pathways using off resonance collisional activation of deprotonated peptides is presented. The dissociation pathways are governed by the site of charge and yield partial C-terminus sequence information in favorable cases. Application of statistical RRKM calculations to these systems allows a qualitative understanding of the energetic changes associated with the observed dissociation processes. The bimolecular reactivity of these species was investigated. Several reactions taking advantage of the nucleophilicity of the deprotonated carboxylic group were observed. This is particularly noteworthy as there are few previously reported instances of bimolecular reactions (other than proton transfer) involving biological species in the gas phase.
The results of the above study identified a homologous system of deprotonated peptides which dissociate with similar activation parameters. This was used as a model system to investigate the effect of molecular size on the collisional activation process. Contrary to the common belief that it is inherently harder to activate large molecules and induce dissociation, it was discovered that molecules with many degrees of freedom dissociate more readily than molecules with fewer degrees of freedom. This is attributed to the ability of these molecules to easily deform and efficiently convert translational energy into internal excitation.
The mechanism of the collisional energy transfer was investigated using trajectory calculations with a molecular mechanics force field. The collisions appear to be impulsive in nature and energy transfer occurs on a timescale similar to a vibrational period. Large molecules have the ability to undergo several encounters with the collision gas in a single collision event, each encounter resulting in a significant amount of internal energy being transferred into internal modes.
A master equation analysis was applied to the off resonance collisional activation process in an attempt to obtain a more quantitative understanding of the dissociation energetics of large molecules. This analysis takes into account all processes contributing to the change in ion internal energy. The primary result of this analysis was the observation that a significant fraction of the ions formed in the collisional activation process have a large internal energy and are slow to collisionally relax under conditions employed in our experiments. A more thorough knowledge of this energy distribution is required before an analysis such as this can be used.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/8gv5-xy57, author = {Murthy, Srihari}, title = {The Gas-Phase Ion Chemistry of Substituted Silanes}, school = {California Institute of Technology}, year = {1993}, doi = {10.7907/8gv5-xy57}, url = {https://resolver.caltech.edu/CaltechTHESIS:01042013-113332582}, abstract = {Ion-molecule reactions in the chlorosilanes, SiHnCl4-n (n = 0-3), and in phenylsilane have been studied by the technique of Fourier transform ion cyclotron resonance spectrometry.
In Chapter 1, the motivations for studying the gas-phase ion chemistry of substituted silanes as well as brief descriptions of the gas phase ion chemistry of the chlorosilanes and of phenylsilane are presented.
Chapter 2 deals with the gas-phase ion chemistry of the chlorosilanes, SiHnCl4-n (n = 0-2). Reactions of the chlorosilyl ions with neutral chlorosilanes and with silane as well as the reactions of the silyl ion with neutral chlorosilanes are presented. The chlorosilyl ions participate in Hˉ, Clˉ transfer reactions and disproportionation reactions. The mechanisms of these reactions are discussed. The Clˉ affinities of the chlorosilyl ions, SiHnCl3-n+ (n = 0-2), lie within a range of 1.2 kcal mol-1 and decrease in the order SiH2Cl+ > SiHCl2+ ≈ SiCl3+. The heats of formation of the chlorosilyl ions are determined.
Chapter 3 deals with the gas-phase ion chemistry of monochlorosilane. The difference in the Hˉ affinities of the ions SiH2Cl+ and SiHCl2+ is determined to be 1.5 ± 0.3 kcal mo-1. The Hˉ affinities of the chlorosilyl ions, SiHnCl3-n+ (n = 0-2), lie within a range of 1.8 kcal mol-1 and decrease in the order SiHCl2+ ≈ SiCl3+ > SiHCl2+. Protonated SiH3Cl is generated by proton transfer from CH5c and is observed to react with SiH3Cl to yield (SiH3)2Cl+.
Chapter 4 deals with the gas-phase ion chemistry of phenylsilane. In analogy with toluene, two (parent – H)+ cations are produced by the electron impact ionization of phenylsilane. These cations are identified to be the phenylsilyl and the silacycloheptatrienyl cations.
Chapter 5 explores the gas-phase ion chemistry of phenylsilane in great detail. Reactions of the parent and fragment ions (created by electron impact ionization) with neutral phenylsilane and with C6D6 are presented. Two structural isomers are identified for the C6H8Si+ cation and three structural isomers are identified for the C6H6Si+ cation. The Hˉ affinity of the phenylsilyl cation is also presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/REZ3-DD85, author = {Irikura, Karl Kensuke Mason}, title = {Gas-Phase Chemistry of Organotransition Metal Ions}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/REZ3-DD85}, url = {https://resolver.caltech.edu/CaltechETD:etd-06202007-111048}, abstract = {
The gas-phase chemistry of many transition metal ions has been investigated by Fourier transform ion cyclotron resonance spectrometry (FTICR). Emphasis is on organometallic chemistry, including an application to geochronology, but inorganic and bio-inorganic systems have also been investigated. Quantum chemical calculations have been performed to address problems in interstellar chemistry and also traditional physical organic chemistry.
Chapter I is concerned with the chemistry of ions OsOn+(n=0-4) with several small molecules, including methane. A wide variety of reactions are observed, including many that are archetypes for fundamental mechanistic processes in organometallic chemistry. In Chapter II, the differences in the gas-phase chemistry of Os+ and Re+ are applied to analytical problems associated with the 187RE-187 dating method, which is important in geology.
Chapter III is a survey of the reactivity of third-row transition metal ions, with emphasis on the unusual reactions involving methane. Fundamental concepts that have proven useful in the interpretation of chemistry in the first and second transition series are also applicable in the third row.
Chapter IV describes the gas-phase synthesis of positive and negative metalloporphyrin ions by reactions of metal-containing ions with porphine vapor. Chapter V presents some possibilities for transition metal catalysis in interstellar clouds. A very low value is calculated for the rate of radiative association of Fe+ and hydrogen atoms, suggesting that transition metal chemistry is not important in these systems.
Chapter VI involves scaling the results of ab initio calculations in order to predict accurate singlet-triplet energy gaps in many substituted carbenes. Observed trends are rationalized using a synergistic bonding model. A simple relationship based upon electronegativity is presented to permit carbene singlet-triplet gaps to be computed using minimal resources, such as a hand calculator.
Chapter VII deals with five different experimental issues that have arisen during FTICR studies of reactive transition metal ions. Difficulties, helpful techniques, and data analysis are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Goddard, William A., III}, } @phdthesis{10.7907/039n-6p75, author = {Sweeney, Robert Joseph}, title = {Hydrogen-Atom Transfer Photochemistry of Tetrakis(µ-pyrophosphito)diplatinate(II)}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/039n-6p75}, url = {https://resolver.caltech.edu/CaltechTHESIS:07162014-152027500}, abstract = {In many senses, the hydrogen-atom transfer reactions observed with the triplet excited state of pyrophosphito-bridged platinum(II) dimers resemble the reactions of organic ketone nπ* states. The first two chapters describe our attempts to understand the reactivity differences between these two chromophores. Reactivity of the metal dimers is strongly regulated by the detailed nature of the ligands that ring the axial site, the hydrogen-abstraction center. A hydrogen-bonded network linking the ligands facilitates H-atom transfer quenching with alcohols through the formation of a hydrogen-bonded complex between the alcohol and a dimer. For substrates of equal C-H bond strength that lack a hydroxyl group (e.g., benzyl hydrocarbons), the quenching rate is several orders of magnitude slower.
The shape and size of the axial site, as determined by the ligands, also discriminate among quenchers by their steric characteristics. Very small quenchers quench slowly because of high entropies of activation, while very large ones have large enthalpic barriers. The two effects find a balance with quenchers of “just the right size.”
The third chapter discusses the design of a mass spectrometer that uses positron annihilation to ionize neutral molecules. The mass spectrometer creates positron-molecule adducts whose annihilation produces fragmentation products that may yield information on the bonding of positrons in such complexes.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Gray, Harry B.}, } @phdthesis{10.7907/6tyj-gy42, author = {Dearden, David Vernell}, 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}, school = {California Institute of Technology}, year = {1989}, doi = {10.7907/6tyj-gy42}, url = {https://resolver.caltech.edu/CaltechETD:etd-02082007-130036}, 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)ₓ⁺ 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⁺-CO bond energies are obtained from the KERDs. Chapter 2 deals with reactions of Fe⁺ and Co⁺ 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⁺, (hydrido)(cyclopropyl)Co⁺ and Co(propene)⁺ structures which do not interconvert on the µs time scale in the gas phase. Chapter 4 deals with the dehydrogenations of cyclic alkanes by Fe⁺ and Co⁺, and shows that, contrary to previous assumptions, statistical energy partitioning occurs in these processes.
Chapters 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.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/sdj1-2y57, author = {Shin, Seung Koo}, title = {Experimental and Theoretical Studies of Silylenes, Silicenium Ions, and Organometallic Reactive Intermediates}, school = {California Institute of Technology}, year = {1989}, doi = {10.7907/sdj1-2y57}, url = {https://resolver.caltech.edu/CaltechTHESIS:11122009-115104264}, abstract = {Fourier transform ion cyclotron resonance spectroscopy has been used to investigate thermochemistry and relative stabilities of silylenes, silaethylene, and silicenium ions in the gas phase. Proton affinities of silylene, methylsilylene and silaethylene have been derived from studies of kinetics and thermochemistry of proton transfer from the corresponding silicenium ions to a series of n-donor bases with well-established gas-phase base strengths. Values of proton affinities combined with the known heats of formation of the corresponding silicenium ions yield heats of formation of silylene, methylsilylene, and silaethylene. Experimental results for the relative stability between methylsilylene and silaethylene are corroborated by ab initio generalized valence bond (GVB)-configuration interaction (CI) calculations which indicate that silaethylene is more stable than methylsilylene. Hydride affinities of the methyl-substituted silicenium ions have been precisely determined from examination of kinetics and equilibria of hydride-transfer reactions of methyl-substituted silanes with various hydrocarbons having well-established gas-phase hydride affinities. The result shows that the silicenium ions are significantly more stable than the corresponding carbonium ions in the gas phase with H⁻ as a reference base.
Photoelectron spectroscopy and mass spectrometry have been employed to identify the gas-phase reactive intermediate in the chiorosilane chemical vapor deposition under the heterogeneous flash vacuum pyrolytic condition. The result indicates that dichlorosilylene and hydrogen chloride are the major gas-phase products and monochlorosilylene is not an abundant gas-phase intermediate.
The ab initio theoretical methods have been used to calculate the equlibrium ge-ometries and singlet-triplet splittings of chlorine- and fluorine-substituted silylenes and methylenes. The GVB-dissociation consistent CI (DCCI) method has been developed to accurately predict singlet-triplet energy gaps within 1 kcal/mol error.
Finally, we have employed Fourier transform ion cyclotron resonance spec-troscopy combined with a line tunable CW CO₂ laser to isolate the coordinatively unsaturated organometallic intermediates and examine structures, reactivities, and spectroscopic properties of the isolated intermediates for the methyl-migratory decarbonylation reaction and ligand displacement reaction. The results show that the CF₃ group is an ideal infrared chromophore to investigate the infrared photochemistry of organometallic complexes, LₙM-CF₃, structures, and reaction mechanisms of their coordinatively unsaturated intermediates containing metal-bonded CF₃ groups. The infrared multiphoton dissociation spectra of the isolated intermediates containing metal-bonded CF₃ group are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/jytn-vs45, author = {Kruppa, Gary Hermann}, title = {Photoelectron Spectroscopy of Reactive Intermediates}, school = {California Institute of Technology}, year = {1988}, doi = {10.7907/jytn-vs45}, url = {https://resolver.caltech.edu/CaltechTHESIS:02202013-105931312}, abstract = {Photoelectron Spectroscopy (PES) has been used to investigate the structure and thermochemistry of a number of alkyl radicals and their corresponding carbonium ions. The radicals have been produced by flash vacuum pyrolysis of alkyl nitrites. The shape of the first band in the photoelectron spectrum of a free radical is related to the structural changes that take place in forming the carbonium ion from the radical. The ionization potentials obtained from the photoelectron spectra of the radicals are combined with gas phase ion thermochemistry data to obtain alkyl radical heats of formation. The thermochemical data thus obtained is used to discuss substituent and structural effects on the stability of radicals and carbonium ions. In many cases the thermolytic decomposition pathways of the alkyl radicals have been elucidated using PES. The application of the PES technique to the analysis of reactive intermediates present in heterogeneous thermolysis mixtures is also discussed.
Chapter 1 presents an introduction to the technique employed in these studies, and a review of the studies performed in this laboratory. Chapter 2 presents results on the thermochemistry and structure of the 1- and 2-adamantyl radicals. The tricyclic 1-adamantyl radical and carbonium ion are important as model bridgehead compounds, and the question of the amount of strain energy caused by the non-planarity of the radical and ion center has been of great interest. The first bands in the photoelectron spectra of the o-, m- and p-methylbenzyl radicals are presented in Chapter 3. The methyl substituent effects on the stabilities of the radicals and ions are discussed.
In Chapter 4 results on investigations of heterogeneous processes in Chemical Vapor Deposition (CVD) systems using the chlorosilanes as feed gases are discussed. SiCl₂ is found to be the major silicon containing reactive intermediate produced by surface reactions at 600 - 1100 °C in CVD systems using dichlorosilane and trichlorosilane as feed gases.
Chapter 5 presents the spectra of the 1- and 2-methylnaphthyl radicals. The relative stabilities of the radicals and carbonium ions are discussed based on proton affinities determined by Fourier transform mass spectrometric equilibrium studies, combined with ionization potentials obtained from photoelectron spectra of the radicals.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/vazp-zt83, author = {Schilling, Jerald Bruce}, title = {Experimental and Theoretical Aspects of Hydrocarbon Activation by Transition Metal Ions in the Gas Phase}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/vazp-zt83}, url = {https://resolver.caltech.edu/CaltechTHESIS:11062009-094101367}, abstract = {
The reactions of several gas-phase metal cations with small hydrocarbons have been studied using ion beam mass spectrometric techniques. We also present several theoretical studies into the sigma bonding between the first and second row transition metal ions and H and CH3.
Chapter II discusses the three cations, europium, praseodymium, and gadolinium in an attempt to understand the role of f electrons in the reactivity of gas-phase lanthanide ions. Eu+ and Pr+ are found to be unreactive with alkanes while Gd+ readily activates both C—H and C—C bonds. The unreactive metals have only one non-4f valence electron. Oxidative addition of a C—H bond to these metals requires a strong bond to an f electron. Gd+, with two non-4f valence electrons need not use the 4f electrons and is seen to be very reactive. This reactivity behavior indicates that the 4f electrons of the lanthanides play little role in alkane activation due to the formation of weak sigma bonds.
In Chapter III and VI, we discuss the reasons for the unreactivity of gas-phase chromium ions. Molybdenum ions which have a very similar electrons structure are found to activate C—H bonds of alkanes. The metal ions are studied from the standpoint of gas-phase reactivity as well as the theoretical description of the bonding in the hydride and dihydride ions. The two metals are found to differ greatly in the strength of the sigma bonds that they form to hydrogen. The oxidative addition of C—H and C—C bonds to Cr+ is endothermic due to the extremely weak bonds formed to the metal ion.
Chapters IV and V report systematic, ab initio, generalized valence bond and configuration interaction calculations on the first and second row transition metal hydrides. The bonding in these systems is seen to depend on a number of factors including: (1) the electronic structure of the metal ions; (2) the sizes of the metal s and d orbitals and the effect on the intrinsic strength of the metal—hydrogen bond; and (3) the mediation of the intrinsic bond strengths by the loss of high spin exchange energy.
Chapter VII presents a theoretical comparison between the metal hydride ions and metal methyl ions. The present theoretical study indicates that for a variety of metal systems, the metal—hydrogen and metal—carbon bonds are very similar, both from the standpoint of metal orbital hybridization as well as bond dissociation energy.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/M9HQ-9749, author = {Kang, Heon}, title = {Gas Phase Studies of Hydrocarbon Oxidation by Chromium Oxide Cation}, school = {California Institute of Technology}, year = {1986}, doi = {10.7907/M9HQ-9749}, url = {https://resolver.caltech.edu/CaltechTHESIS:07262010-154826937}, 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.
Chapter 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.
Chapter 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.
Chapter 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.
Chapter 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.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/3047-z490, author = {Tolbert, Margaret A.}, title = {Mechanisms and Energetics of Alkane Activation by Transition Metal Ions in the Gas Phase}, school = {California Institute of Technology}, year = {1986}, doi = {10.7907/3047-z490}, url = {https://resolver.caltech.edu/CaltechTHESIS:10282019-140307646}, abstract = {The mechanisms and energetics of alkane activation by transition metal ions in the gas phase are studied using an ion beam apparatus. These investigations concentrate on the reactivity of several early first row transition metal ions (Sc+, Ti+, V+) and the second row group 8-10 metal ions (Ru+, Rh+, Pd+). The reaction mechanisms are probed using deuterium labelled alkanes. Experimental and theoretical metal-ligand bond dissociation energies are used to help interpret the observed metal ion reactivities.
Chapter II provides a detailed study of the reactions of Ru+, Rh+ and Pd+ with alkanes. The reactivity observed is contrasted to that of their first row congeners Fe+, Co+ and Ni+.
Chapter III presents a determination of the heterolytic, M+-H-, and homolytic, M-H, bond dissociation energies for the first and second row group 8-10 metals. A correlation is found between the homolytic bond energies and the metal atom promotion energy to a state derived from an s1dn electronic configuration.
Chapter IV examines the reactions of Ti+ and V+ with alkanes and deuterium labelled alkanes. Dehydrogenation mechanisms and deuterium isotope effects are explored.
Chapter V reports the unusual reactivity of Sc+ with alkanes. The ability of Sc+ to form two strong metal-ligand sigma bonds results in alkane activation processes which are not observed for most other transition metal ions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/f9mq-vz30, author = {Flanagan, Dorothy Jean}, title = {The Angular Resolved Photoelectron Spectroscopy of Various Polyatomic Molecular Systems}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/f9mq-vz30}, url = {https://resolver.caltech.edu/CaltechTHESIS:02052019-112244749}, 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.
The 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.
Photoelectron 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 β observed in studies of the methylated ethenes.
Additionally, the semi-empirical rule that the β values of π orbitals are higher than for σ orbitals was violated in this series. Acetylene and propyne possess σ orbital with β values significantly higher than the π orbitals.
Two 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.
The 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.
This 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 πC = 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.
Lastly, 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.
There 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.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/r4n1-8762, author = {Garvey, James F.}, title = {The Production and Characterization of an Intense Hyperthermal Beam of H₃ Molecules and of H Atoms}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/r4n1-8762}, url = {https://resolver.caltech.edu/CaltechTHESIS:02132012-111043915}, abstract = {The simplest bimolecular reaction involving neutral reagents is the reaction
H + H2 → H2 + H.
This 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.
In 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.
In 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 µsec 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.
In 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.
Section 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.
Appendix 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 (ν = 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.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/YP9D-ED80, author = {Koerting, Charles Frederick}, title = {Variable-Angle Electron Spectroscopic Studies of Various Polyatomic Molecular Systems}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/YP9D-ED80}, url = {https://resolver.caltech.edu/CaltechTHESIS:02132014-084828083}, 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° to 90°. 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° to 90°. 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.
The 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 π → π, N → 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 π → 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 π → π, N → T, and N → V as well as the π → 3s excitation are discussed and compared to those observed in the methyl- and fluoro-substituted ethylenes.
The 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 → 1A1g, 2t2g(π) → 3t2g(π*) 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 → 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.
A number of exploratory studies have been performed. The π → π*, N → T, singlet → 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° 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.
Variable-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, β, along with those measured for cyclopropane were used to confirm the orbital correlations and photoelectron band assignments. No high values of β similar to those expected for alkene π orbitals were observed for the Walsh or Forster-Coulson-Moffit type orbitals.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/b03t-1z96, author = {Brinza, David Edward}, title = {I. Millimeter Microwave Spectroscopy of Radicals. II. Laser Spectroscopy of the Van der Waals Molecule Ne-Cl₂}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/b03t-1z96}, url = {https://resolver.caltech.edu/CaltechTHESIS:10242018-130045424}, abstract = {The temperature dependence of the linewidth parameter for the pressure broadening of ClO rotational transitions was investigated. As determined from millimeter microwave spectroscopy, the value of the linewidth parameter at 218 K is 4.44±0.23 MHz/torr. The width parameter varies according to T-0.75±0.2 over the temperature range 200-350 K. A similar study was carried out for oxygen self-broadening and broadening by nitrogen. The stronger temperature dependence for the self-broadened case suggests a resonant spin-flip or exchange process is important in the collisional broadening.
The measurement of microwave spectra of the CS radical, as produced in the ArF excimer laser photolysis (193 nm) of CS2 was attempted. No spectra for the vibrationally excited CS molecules produced in the photolysis could be observed, presumably due to relatively slow rotational relaxation of the CS fragment.
The van der Waals molecule Ne-Cl2 has been studied by molecular beam laser spectroscopy. Fluorescence features ~6 cm-1 to higher energy of the Cl2B-X band origins are attributed to Ne-Cl2. Band shape analysis supports a T-shaped molecular structure. The metastable vibrationally excited molecule Ne-Cl2(X1 Σ+, ν" = 1) has been spectroscopically observed. The time-of-flight from the nozzle indicates the lifetime of the complex to be greater than 10-5 sec.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/n43s-1339, author = {Casassa, Michael Paul}, title = {Infrared Photodissociation of Van der Waals Molecules}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/n43s-1339}, url = {https://resolver.caltech.edu/CaltechTHESIS:10262018-123200794}, 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.
Van 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 ν7 frequency of free ethylene correspond to lifetimes ranging from 0. 44 psec for (C2H4)2 to greater than 10 psec for Ne•C2H4. These are attributed to vibrational predissociation constrained by conservation of angular momentum. Other conceivable broadening mechanisms are discussed.
Spectra obtained by exciting the ν7 mode in different types of ethylene clusters are quite dissimilar. Lineshape analysis indicates that the ν7 transition in (C2H4)2 occurs as a hybrid band. The same transition in (C2H4·HF 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 ν7 absorption. All of the ethylene clusters exhibit blue shifts and intensity enhancement, as compared to ν7 absorption by free ethylene, which are attributed largely to electrostatic interactions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/vmgw-qf86, author = {Gleeson, James William}, title = {I. A Nuclear Magnetic Resonance Study of Metal Carbonlys in the Solid State, and II. Studies of the Surface Chemistry of Rhodium Supported on Alumina}, school = {California Institute of Technology}, year = {1982}, doi = {10.7907/vmgw-qf86}, url = {https://resolver.caltech.edu/CaltechTHESIS:05152018-092853858}, abstract = {
Part I
The principal components of the 13C nuclear magnetic resonance chemical shift tensors of metal carbonyls containing between one and six metal atoms were determined from the powder patterns of the solid compounds. The tensors of terminally-bound CO groups are highly anisotropic (380 ± 60 ppm) and nearly axially symmetric. The tensors of bridging CO groups are much less anisotropic, due to significant asymmetry in the electron orbitals about the CO internuclear axis. The tensors vary only slightly for different transition metals. There is no intramolecular rearrangement of the metal carbonyls in the solid state at frequencies ≳ 10kHz, except in Fe3(CO)12.
Part II
The surface chemistry of rhodium supported on alumina was studied using infrared spectroscopy and quantitative measurements of the gases adsorbed and evolved during various procedures. First, the behavior of alumina-supported Rh upon heating in the presence of CO, CO2, O2 and H2 was studied. The loss in the capacity to adsorb CO after heating to 525 K increases in the order O2, H2, vacuum < CO2 < CO. Upon heating in CO, some CO is oxidized to CO2 with oxygen from the surface, while the dicarbonyl-forming RhI is reduced to Rh°. The Rh° agglomerates, accounting for the substantial loss in capacity to adsorb CO. Upon heating in CO2, the dicarbonyl-forming RhI is also deactivated. There is little loss in the capacity to adsorb CO upon heating in H2, O2 or vacuum.
Second, the adsorption of H2S and its interaction with CO on Rh supported on alumina was studied. The dissociation of H2S on the Rh at 300 K produces H2 and is inhibited by preadsorbed CO. Rh also facilitates the reaction of H2S with surface oxygen below or at 373 K, in which water is produced. After exposure of the Rh to H2S, CO adsorbs in the linear, but not in the dicarbonyl or bridging modes. Exposure of a CO-precovered surface to H2S displaces much of the bridging CO, but only slowly removes the dicarbonyl and linear CO. Exposure to H2S strongly inhibits the removal of adsorbed CO by O2, but exchange of adsorbed and gas phase CO occurs readily.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/XKHS-2M38, author = {Stevens, Amy Elizabeth}, title = {Fundamental Studies of Reactive Intermediates in Organometallic Chemistry}, school = {California Institute of Technology}, year = {1981}, doi = {10.7907/XKHS-2M38}, url = {https://resolver.caltech.edu/CaltechTHESIS:04262018-131940882}, abstract = {The techniques of ion cyclotron resonance spectroscopy and photoionization-mass spectrometry are used to characterize the thermochemistry and reactivity of transition metal and organometallic species in the gas-phase. Chapter I gives an introduction emphasizing the need for physical studies of these compounds. An assessment of the differences in chemical properties and reactivity between the gas phase and solution is also made.
Chapter II details the properties and reactions of (CO)5MnR (R = H, CH3) determined using the techniques of ion cyclotron resonance spectroscopy. An examination of the products (CO)5Mn(R)H+, (CO)4Mn(R)H+, and (CO)5Mn+ which result from proton transfer with varying exothermicity to (CO)5MnR permits several thermochemical and mechanistic inferences. In particular the prcton affinities of these species are derived and the mechanism of reductive elimination of RH from the conjugate acids is detailed.
An examination of processes involving negative ions yields the heterolytic bond energies D[(CO)5Mn--R+]. The hydride is found to be an exceptionally strong acid in the gas phase.
Positive and negative ion mass spectra and ion-molecule reactions are reported briefly.
Chapter III presents the results of an ion cyclotron-resonance trapped ion study of the kinetics of proton transfer from MnH+ (formed as a fragment ion from HMn(CO)5 by electron impact) to bases of varying strength. Deprotonation is rapid with bases whose proton affinity exceeds 196 ± 3 kcal mol-1. Using this value for PA[Mn] yields the homolytic bond dissociation energy D[Mn+-H] = 53 ± 3 kcal mol-1.
In Chapter IV the results of a photoionization mass spectrometric determination of the ionization potentials and selected fragment ion appearance potentials of (CO)5MnR where R = H , CH3, CH2F, CHF2 and CF3 are presented. A comparison of the appearance potential of (CO)5Mn+ from all five species yields the metal-carbon bond dissociation energies relative to the metal-hydrogen bond dissociation energy with no additional thermochemical data. Using the literature value D0[(CO)5Mn-H ] = 57 kcal/mol gives D0[(CO)5Mn-R] = 44, 32, 33, and 42 kcal/mol, respectively. Fragmentation thresholds for the metal carbene fragment ions (Co)5MnCXY+ where X, Y = H or F are analyzed to yield the fluoride and hydride affinities of these species. Ion cyclotron resonance spectroscopy is used to examine hydride and fluoride transfer react ions involving these carbenes to corroborate the photoionization data. The carbene bond dissociation energies D0[(CO)5Mn+-CXY] decrease from 104 to 98 to 82 kcal/moL with successive substitution of F for H .
In Chapter V the proton affinities of twenty organotransition metal complexes in the gas phase are reported. Combined with adiabatic ionization potentials, these data yield metal-hydrogen hemolytic bond energies for the sixteen species for which protonation occurs on the metal center. These bond energies range from 53 to 87 kcal/mol. Bond energies increase on going from a first-row complex to its second-row homologue, but no increase is seen on going to the third-row metal. The metal-hydrogen bond energy decreases markedly with increasing oxidation state of the same metal. Comparison to isoelectronic neutral complexes is made.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/8kc4-gq42, author = {Rappé, Anthony Kay}, title = {Theoretical Studies of Homogeneous Catalysis by Transition Metal Complexes}, school = {California Institute of Technology}, year = {1981}, doi = {10.7907/8kc4-gq42}, url = {https://resolver.caltech.edu/CaltechETD:etd-02032005-112022}, abstract = {
CHAPTER 1: Extensive ab initio calculations (double zeta plus polarization function basis with correlated wavefunctions) on the oxidation of hydrocarbons by chromyl chloride are combined with standard thermochemical methods to predict the energetics for oxidation of alkanes, alcohols, and alkenes. Additional results are presented on the analogous oxidations by molybdyl chloride. A common feature of all these reactions is identified and explained.
CHAPTER 2: Extensive ab initio calculations (double zeta plus polarization function basis with correlated wavefunctions) on the olefin metathesis reaction with high valent Mo and W catalysts are combined with standard thermochemical methods to predict the energetics of potential intermediates. The active catalyst is identified and explained together with several subsidiary features of the reaction manifold.
CHAPTER 3: A unifying generalized valence bond view of transition metal ligand bonding is presented as well as the energetics and structural characteristics of several ligand types. Additionally, the energetics for several ligand exchange reactions of potential synthetic utility are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/cggh-sb21, author = {Woodin, Richard Lawrence}, title = {Ion cyclotron resonance studies of vibrationally excited ions. I. Low intensity multiphoton dissociation of gas phase ions using CW CO_2 laser radiation. II. Infrared radiative stabilization of energized species in the gas phase.}, school = {California Institute of Technology}, year = {1979}, doi = {10.7907/cggh-sb21}, url = {https://resolver.caltech.edu/CaltechTHESIS:11052009-133235754}, abstract = {This thesis is divided into two general topics; vibrational excitation of gas phase molecules using cw CO_2 laser radiation (Chapters II and III) and stabilization of chemically activated species by infrared radiative emission (Chapters IV-VI). Chapter I is a brief introduction to the topics discussed in Chapters II- VI. Multiphoton dissociation of molecules is observed using low intensity (1-100 W cm^(-2)) cw CO_2 laser radiation. Ion cyclotron resonance techniques allow gas phase ions to be stored and irradiated for times approaching several seconds prior to mass analysis. Chapter II describes multiphoton dissociation of ions derived from diethyl ether [(C_2H_5)_2O] while Chapter III describes multiphoton dissociation of C_3F_6^+ from perfluoropropylene (C_3F_6). Energy fluence thresholds and cross-sections for multiphoton dissociation measured using low intensity radiation qualitatively agree with similar measurements using megawatt pulsed infrared lasers. For all ions which photodissociate only the lowest activation energy process is observed. Effects of bimolecular interactions, varying laser intensity, and laser wavelength on photodissociation probabilities are explored. At high pressures collisions are observed to deactivate vibrationally excited ions. At low pressures, however, C_3F_6^+ photodissociation is enhanced by collisions. The consequences of collisional enhancement of multiphoton absorption are discussed. ICR techniques are uniquely suited for studying ion-molecule reactions under nearly collisionless conditions. Chapters IV and V discuss direct association reactions of Li^+ with (C_2H_5)_2CO, CH_3COC_2H_5, (CH_3)_2CO, (CD_3)2CO, CH_3CHO, and H_2CO at pressures low enough (< 10^(-6) Torr) to preclude collisional stabilization of the chemically activated adduct. The stabilization mechanism is assumed to be via infrared emission, and calculated attachment rates are in good agreement with experiment. In experiments similar to those described above, rates of direct electron attachment to C_6F_6 (perfluorobenzene), C_7F_8 (perfluorotoluene), c-C_4F_8 (perfluorocyclobutane), and C_7F(14) (perfluoromethylcyclohexane) are measured at low pressure by ICR techniques. Rate constants measured by ICR are found to be one to two orders of magnitudes smaller than high pressure swarm measurements. The results are discussed in terms of radiative stabilization at low pressure versus collisional stabilization at high pressure. Combination of data from time-of-flight, electron beam-swarm, and ICR experiments allows estimates of infrared radiative lifetimes to be made. These fall in the range 0. 4-3. 0 msec, which are typical of infrared radiative processes. Data are also presented for dissociative electron attachment of CCl_4.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/zppe-fp18, author = {Houle, Frances Anne}, title = {Studies of alkyl free radicals and reaction mechanisms by photoelectron spectroscopy}, school = {California Institute of Technology}, year = {1979}, doi = {10.7907/zppe-fp18}, url = {https://resolver.caltech.edu/CaltechTHESIS:11022009-081650291}, abstract = {Application of vacuum ultraviolet photoelectron spectroscopy (UPS) to the study of simple alkyl free radicals and organic reaction mechanisms is described. A brief overview of the field of UPS of chemical transients, including a survey of the relevent literature, and a general introduction to topics covered in this thesis are given in Chapter 1. Chapters 2, 4 and 5 present results of UPS investigations of the first photoelectron bands of alkyl radicals produced by pyrolysis of the corresponding alkyl nitrites. Spectra have been obtained for methyl, ethyl, 1-propyl, 2-propyl, tert-butyl, cyclopentyl, cyclohexyl and 2-norbornyl radicals. Adiabatic ionization potentials determined for these species are used to calculate heats of formation of the ions, heterolytic bond dissociation energies of the corresponding alkanes, and proton affinities of the corresponding olefins. The shapes of the bands are discussed qualitatively in terms of structural differences between neutrals and positive ions. Chapter 3 is a discussion of the lowest energy conformations of ethyl and tert-butyl radicals. In particular, ESR and theoretical results from the literature are used to discuss the question of the planarity of alkyl radical centers. Chapters 4 and 6 present results of studies of the thermal decomposition mechanisms of 2-norbornyl, cyclopentyl and cyclohexyl radicals. Pyrolysis of the radicals is readily observed under the conditions necessary for their generation. The mechanisms deduced from the spectra are compared to those resulting from studies using classical techniques. In Chapter 7, experiments designed to assess the fate of reaction exothermicity in the pyrolysis of some strained azo compounds are described. The results indicate that very little of the available energy is released to vibration of the N_2 fragment. The implications of this observation for the transition states of the reactions that were studied are discussed.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/RYFA-1T76, author = {Corderman, Reed Roeder}, title = {Ion cyclotron resonance studies of ionrganic molecules in the gas phase. Organotransition metal complexes. Chain reactions involving ionic intermediates}, school = {California Institute of Technology}, year = {1977}, doi = {10.7907/RYFA-1T76}, url = {https://resolver.caltech.edu/CaltechETD:etd-09202007-075658}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
A brief introduction (Chapter 1) gives a general overview of the results presented in this thesis, and is followed by five chapters which concern ion cyclotron resonance spectroscopy (ICR) studies of transition metal complexes, trifluorophosphine, and methylsilanes in the gas phase. An ancillary study on the photoionization mass spectrometry (PIMS) of the methylsilanes is also included.
Chapter II discusses the gas phase ion chemistry of ([eta superscript 5] - C5H5)NiNO. The dissociative bond energies, D(B-CpNi[superscript +]) […], are obtained by measuring equilibrium constants for reactions involving CpNi[superscript +] transfer between appropriate base pairs. A wide variety of reactions effected by CpNi[superscript +], including dehydrohalogenation, dehydration, dehydrogenation, decarbonylation, and alkylation processes are observed, and reaction mechanisms proposed.
Chapter III presents a detailed study of the sequential alkylation of CpNi[superscript +] and CpFe[superscript +] by d3-methyl bromide. A reaction mechanism involving oxidative addition of the metal to the weak carbon-bromine [sigma]-bond is presented.
The first observed example of a ligand displacement reaction involving an anionic transition metal complex, in which PF3 displaces CO from CpCo(CO)[superscript -], is reported in Chapter IV. This result leads directly to the conclusion that PF3 is a stronger [pi]-acceptor ligand than CO towards CpCo[superscript -] in the gas phase. Additionally, the negative ion chemistry of CpCo(CO)2 both alone and in mixtures with various ligands is presented.
The gas phase basicity, or proton affinity, of phosphorus tri-fluoride is determined in Chapter V. The results are discussed in terms of contributions from inductive and hyperconjugative interactions involving p[subscript pi]-d[subscript pi] bonding in HPF3[superscript +]. Ion-molecule reactions of mixtures of PF3 with SiF4, BF3, SF6, NF3, CH3F, and (CH3)2CO are briefly considered; various thermochemical considerations are used to determine the energetics of formation of the PF2[superscript +], PF4[superscript +], and CH3PF3[superscript +] ions observed in these mixtures.
Several examples of gas phase chain reaction which proceed through ionic intermediates are presented in Chapter VI. Chain propagation reactions involve hydride and fluoride transfer between pairs of siliconium ions R1[superscript +] and carbonium ions R2[superscript +], for which D(R1[superscript +]-F[superscript -]) […] D(R2[superscript +]-F[superscript -]) and D(R1[superscript +]-H[superscript -])[…] D(R2[superscript +]-H[superscript -]).
Photoionization efficiency for the low energy fragment ions (P-H)[superscript +], (P-H2)[superscript +], and (P-CH4)[superscript +] for the series of methylsilanes, (CH3)nH4-nSi (n = 0-3), are reported in Chapter VII. Appearance potentials for the (P-H)[superscript + siliconium ion fragments afford accurate calculation of the hydride affinities, D(R3Si[superscript +] -H[superscript -]) of these species.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/HMVE-Q508, author = {Freiser, Benjamin Sherman}, title = {Photochemical investigations of ions in the gas phase utilizing ion cyclotron resonance spectroscopy}, school = {California Institute of Technology}, year = {1977}, doi = {10.7907/HMVE-Q508}, url = {https://resolver.caltech.edu/CaltechETD:etd-02242009-110155}, abstract = {The photochemistry and photophysical processes of a broad range of ions have been studied in the gas phase using ion cyclotron resonance techniques. A discussion summarizing much of this work, and two papers on related topics are presented. In paper I, “Acid-Base Properties of Molecules in Excited Electronic States Utilizing Ion Cyclotron Resonance Spectroscopy”, a general method is described for obtaining excited state acid-base properties of molecules and ions in the gas Phase which utilizes ion cyclotron resonance spectroscopy for studying photochemical processes involving ions. These processes, including photodissociation and photodetachment, yield in favorable instances, electronic excitation energies of ions. A comparison of the excitation energies of a base B with the corresponding acid-base complex AB yields the excited state basicity of B. Similarly, a comparison of the excitation energies of a chromophoric acid A with the complex AB yields information about the excited state acidity of A. Studies of the first type are described using the reference acids H[superscript +] and Li[superscript +] with the bases C6H5X (X = H, CN, NH2, CHO, COCH3, NO2, OCH3, O[superscript -], and S[superscript -) pyridine, and ferrocene. In several instances photodissociation spectra of solvated acid-base complexes of the type BLib[with a + above the L] have been obtained and analyzed to determine the effects of further solvation on the excitation spectra of these complexes. A comparison of the gas phase excitation spectra of a number of ions to their solution absorption is made. Studies of the second type (excited state acidities) are described using the reference base H[superscript -] with the acids C6H5CO[superscript +] and C6H5CHOH[superscript +]. Calculated changes in acidity and basicity are used to infer changes in electron distributions and dipole moments for excited states, and yield insight into the types of transitions involved. In particular, these studies are used to assess the controversial role played by intra-molecular charge transfer in the lowest two singlet π→π* transitions of monosubstituted benzenes. These results are compared with findings from related experiments and calculations when available. Paper II, entitled “Electron Impact Dissociation of Cyanobenzene Radical Cations by Ion Cyclotron Resonance Spectroscopy”, describes using trapped ion cyclotron resonance spectroscopy for the first time to study the electron impact dissociation of ions. Fragmentation of C6H5CN[superscript +] to produce C6H4[superscript +] and HCN is observed to occur at low electron energies (3-9 eV). The extent of dissociation is observed to be linear in emission current, rising from a threshold at 3.0 ± 0.5 eV to a maximum cross section estimated to be 6 Å[superscript 2] at 7.5 ± 0.5 eV. The implications of these results are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/mgxv-k439, author = {Williamson, Ashley Deas}, title = {Investigation of kinetics and thermochemistry of ion-molecule reactions using photoionization mass spectrometry}, school = {California Institute of Technology}, year = {1976}, doi = {10.7907/mgxv-k439}, url = {https://resolver.caltech.edu/CaltechTHESIS:01232017-162540529}, abstract = {Chapter I introduces the methodology of photoionization mass spectrometry and lists common applications, including study of ionmolecule reactions. A major advantage of photoionization in the study of ion chemistry lies in the favorable photoionization threshold laws, which frequently permit accurate knowledge of the internal energy distribution of reactant ions. Study of reactions as this distribution is varied allows measurement of the effects of reactant ion internal energy on the reaction kinetics. The photoionization mass spectrometer consists of a discharge lamp, a one-meter normal incidence vacuum monochromator, and a medium pressure quadrupole mass spectrometer. The instrument and its operating conditions are detailed.
Chapter II contains a photoionization study of the reactions of the molecular ion in vinyl fluoride to yield the ionic products C3H3F2+, C3H4F+, and C3H5+. Quantitative measurements are reported of the effect of the vibrational state of the reactant ion on the product distribution and overall reaction cross section. Reaction cross sections for all three channels decrease with reactant internal energy. The effect on the reaction pathway producing C3H3F2+ is especially pronounced, with 0.19 eV of vibrational excitation being sufficient to reduce the reaction probability by 80%. Deactivation of vibrationally excited reactant ions competes with the reaction and is shown to be an efficient process.
Chapter III details a study of the major ion-molecule reaction pathways in ketene and ketene-d2 by photoionization mass spectrometry and ion cyclotron resonance spectroscopy. For processes involving the molecular ion, the variation of reaction cross section with ion vibrational state is pronounced. The threshold determined for the endothermic process CH2CO+ + CH2CO → C2H4+ + 2CO provides a novel confirmation of the recent redetermination of the heat of formation of ketene.
In Chapter IV photoionization efficiency data are presented for the parent and major fragment ions in 2,2-difluoropropane and 2-fluoropropane. Appearance potentials for CH3 and CH4 loss may be used to relate the heats of formation of the olefin radical cations and fluorinated ethyl carbonium ions to the parent neutral and to one another. A thermochemical cycle allows determination of the proton affinities of vinyl fluoride and 1,1-difluoroethylene. The fragmentation thresholds in 2-fluoropropane appear to be too high by 7-9 kcal/mole. standard heats of formation determined by this study are: (CH3)2CF2, -129.8 ± 3.0 kcal/mole; CH3CF2+, 108.5 ± 3.2 kcal/mole; (CH3)2CF+, 138.0 ± 1.6 kcal/ mole; CH3CHF+, 162.6 ± 1.1 kcal/mole.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/32NW-ER15, author = {Staley, Ralph Horton}, title = {Studies of acid-base ion-molecule chemistry using ion cyclotron resonance techniques and photoelectron spectroscopy}, school = {California Institute of Technology}, year = {1976}, doi = {10.7907/32NW-ER15}, url = {https://resolver.caltech.edu/CaltechTHESIS:11052009-095120323}, abstract = {Thermochemical properties related to molecular basicity are examined for series of substituted amines and nitriles using ion cyclotron resonance techniques and photoelectron spectroscopy. Proton affinities PA(B), defined for a base B as the heterolytic bond dissociation energy for removing a proton from the conjugate acid BH^+, and adiabatic ionization potentials, IP(B), are determined. In previously examined series of bases linear relationships have been established between proton affinities and adiabatic first ionization potentials which correspond to removal of an electron from a lone pair localized at the site of protonation. Nitrile proton affinities are found to be linearly related not to the first CN π ionization potentials but rather to the adiabatic N lone pair σ ionization potentials at higher energy. This relationship provides a useful chemical means for the assignment of bands in photoelectron spectra; specific examples are considered and assigned. Homolytic bond dissociation energies D(B^+-H) are obtained using the relation PA(B)-D(B^+-H) = IP(H)-IP(B). Systematic effects of substitution on PA(B), D(B^+-H), and IP(B) are identified and discussed in terms of the intrinsic factors affecting molecular basicity. Ion cyclotron resonance techniques are also used to measure relative heterolytic bond dissociation energies D(R+-Br-) in the gas phase for a series of alkali cations, alkyl carbenium ions, acylcations, and cyclic halonium ions. D(R+-Br-) for adamantyl cation is found to be less than for tert-butyl cation. A proton affinity for norbornene of D(B-H^+) = 198.2 ± 2 kcal/mol is determined from which D(R+-Br-) = 146.8 ± 2.3 kcal/mol is calculated for norbornyl cation, 14 kcal/mol less than for cyclo-pentyl cation. Relative enthalpies of solvation are estimated via appropriate thermochemical cycles by combining the gas phase data with heats of ionization in fluorosulfuric acid. The results show that solvation enthalpies are related to ion size with smaller ions being better solvated. Relative stabilities of cyclic bromonium ions are the same in the gas phase and solution. Stability increases with increasing ring size and in the three-membered rings with methyl substitution. However, solvent has an appreciable effect in attenuating the observed range.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/VAP4-RG14, author = {Foster, Michael Stewart}, title = {Properties and reactions of some inorganic and organometallic compounds in the gas phase}, school = {California Institute of Technology}, year = {1975}, doi = {10.7907/VAP4-RG14}, url = {https://resolver.caltech.edu/CaltechETD:etd-09202007-080247}, abstract = {The gas-phase ion-molecule reactions occurring in several inorganic and organometallic systems have been examined by ion cyclotron resonance (icr) spectroscopy.
Electron attachment to sulfur hexafluoride under collision-free conditions has been shown to produce stable SF6[superscript -] by a radiative de-excitation process. Halide ion transfer reactions involving anions derived from several covalent sulfur halides produce the hydrogen dihalide anions, XHY[superscript -] (X, Y = halogen), and other interesting anionic dimers. These results have important implications for radiolysis experiments which employ SF6 as an electron scavenger.
The ion-molecule reactions of iron pentacarbonyl are characterized by the formation of polynuclear clusters containing up to four iron atoms. Extensive carbon monoxide replacement reactions are also observed with a wide variety of [sigma]- and [pi]-bonding ligands. Fe(CO)5 is shown to have a proton affinity slightly less than that of ammonia.
The fragment ions derived from ferrocene undergo charge exchange with the parent neutral and condense with it to form Fe2(C5H5)3[superscript +]. The proton affinity of ferrocene is very high, the molecule being only slightly less basic than methylamine. Some general conclusions are reached about the concept of transition metal basicity.
The proton affinity of hydrogen fluoride has been determined as 1 kcal/mole less than that of nitrogen. The anomalous behavior of HF relative to the other hydrogen halides is discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/BJCA-7136, author = {McMahon, Terrance Brian}, title = {Trapped ion cyclotron resonance studies of ion-molecule reactions}, school = {California Institute of Technology}, year = {1974}, doi = {10.7907/BJCA-7136}, url = {https://resolver.caltech.edu/CaltechETD:etd-01222009-092248}, abstract = {Techniques and instrumentation have been developed which permit trapping of ions in the source region of an ion cyclotron resonance cell. These techniques have been used to determined rates of ion-molecule reactions and to observe gas phase ion-molecule equilibria.
The rate constants of a number of symmetric charge exchange and proton transfer reactions in simple molecules have been determined and related to theoretical models of ion-molecule reaction. In addition, the role of a symmetric reaction in competition with exothermic reaction channels has been discussed.
The rates of symmetric proton and deuteron transfer in a number of simple alkyl alcohols and amines have also been obtained. These reactions have been related to de-excitation mechanisms of excited ions.
Gas phase ion-molecule equilibria have been examined to obtain substituent effects on such properties as gas phase basicity, acidity and carbonium ion stabilities.
Finally, the ion-molecule reactions of a cyclic ether, trimethylene oxide, have been examined to illustrate the wide range of information available through ion cyclotron resonance experiments.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/FMJE-KV22, author = {Ridge, Douglas Poll}, title = {I. Studies of Collision Broadening of Ion Cyclotron Resonance Lineshapes. II. Studies of the Gas Phase Ion Chemistry of Fluoroethanes}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/FMJE-KV22}, url = {https://resolver.caltech.edu/CaltechTHESIS:07232018-123515101}, abstract = {In Section I theoretical calculations of gas phase ion mobilities are reviewed. The results of measurements of ion cyclotron resonance linewidths of ions in methane and ions in hydrogen are presented. The relationship between ion mobilities, collision frequencies and ion cyclotron resonance linewidths is reviewed. The results of the linewidth measurements are compared with DC mobility measurements and theoretical calculations of the mobility. The results of previous ion cyclotron resonance linewidth measurements are in serious disagreement with DC mobility measurements. The results of the present study, however, agree well with recent mobility measurements. Except for H+ and H3+; in hydrogen the results of the linewidth measurements are consistent with the theory of Mason and Schamp which is based on a three term 12-6.-4 ion molecule interaction potential. It is concluded that weak chemical bonding occurs between hydrocarbon ions and methane and that the anisotropy of the H2 molecule plays a significant role in determining the cyclotron resonance linewidths of ions in hydrogen. The parameters which determine the 12-6-4 potentials which best characterize the interaction between the ion-neutral pairs studied are estimated. It is concluded that the interaction of H+ and H3+ with H2 are too energetic to be adequately represented by a 12-6-4 potential. Measurements of the linewidths of Na+ ions in the C3H6O isomers are found to increase linearly with dipole moment in quantitative agreement with a simple model. The implications of this result are discussed.
In Section II a series of fluoride transfer reactions between fluoroalkyl cations and fluoroalkanes in the gas phase are described. In one case (CH3CHF+ + CH3CF3 → CH3CF+2 + CH3CHF+2) equilibrium is observed so that a free energy change can be assigned from the final ratio of the ionic products. From this result and from observations of competitive fluoride transfer reactions in mixtures of fluoroalkanes a sequence of fluoride affinities of fluoroalkyl cations is deduced (the fluoride affinity of R+ is -ΔH for the reaction R+ + F- → RF). Including the results of previous studies the sequence in order of decreasing fluoride affinities is C2F+5 > CF+3 > CH+3 > CH2F+ > CHF+2 > CHF2CHF+ > CH2FCHF+ > CH3CF+2 > CH3CHF+ > C2H+5. The effects of fluorine substituents on ethyl cation stability are discussed. A simple electrostatic model is proposed to account for the destabilization of fluoroethyl cations by β fluorine substituents.
The base induced elimination of HX from alkyl halides (RX) in the gas phase is proposed and its observation reported. The reaction CH3O- + C2H5F → CH3OHF- + C2H4 is shown by isotopic labelling and kinetic studies to be a based induced 1,2 elimination. Analogous reactions are observed between CH3O- and CH3CHF2, CH3CF3, CH2FCHF2, and CHF2CHF2. It also appears that F- reacts with fluoroethanes in an analogous way. Other substrates from which bases appear to eliminate HX are β-chloroethanol, ethylene bromohydrin and CH3CC13. Proton transfer between fluoroethanes and CH3O- is also observed. The fluoroethyl anions formed transfer F- to the parent fluoroethanes. The thermochemical consequences of the observed reactions with regard to the binding in species of the type XHY- and with regard to the electron affinities of the fluoroethyl anions are discussed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/0b6f-h333, author = {Morton, Thomas Hellman}, title = {Organic Reactions in the Gas Phase. I. The Thermal Rearrangement of 3, 3-Dimethylcyclopropene. II. Interaction of Remote Functional Groups in the Ion Chemistry of Bifunctional Ethers}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/0b6f-h333}, url = {https://resolver.caltech.edu/CaltechTHESIS:01312018-114130193}, abstract = {
PART I: The Thermal Rearrangement of 3, 3-Dimethylcyclopropene
The thermal rearrangement of 3, 3-dimethylcyclopropene was investigated by entering the energy surface for the reaction by two routes: thermal isomerization of the cyclopropene and pyrolysis of a diazo compound precursor, 3-methyl-1-diazo-2-butene. The products from both reactions are identical; however the proportions vary greatly. Greater than 95% of the product from the diazo compound is the cyclopropene, and the remainder of the product is isoprene and isopropylacetylene in a 5:2 ratio, with trace gem-dimethylallene. The products from isomerization of the cyclopropene are isopropylacetylene, isoprene, and gem-dimethylallene in a ratio of 500:50:1. From these data it is concluded that two intermediates exist for the isomerization, gem-dimethylvinylcarbene, (CH3)2C=CH CH, and a 90° rotamer, designated as a diradical, (CH3)2ĊCH=ĊH. Relative rates of interconversion and cyclization and an energy surface are determined and the results are compared with Huckel and CNDO/2 calculations on vinylcarbene.
PART II. Interaction of Remote Functional Groups in the Ion Chemistry of Bifunctional Ethers
An Ion Cyclotron Resonance examination of bifunctional ethers of the form CH3O(CH2)nOR, where n = 1 - 6 and R = H, CH3, or C2H5, reveals a large number of mass spectral processes and ion-molecule reactions in which the interaction of remote functional groups plays a prominent role. Chainlength effects are particularly pronounced: 6-member cyclic intermediates are inf erred in rarrangements of odd electron species, while larger cycles appear pref erred in rearrangements of many even electron species.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Bergman, Robert G.}, } @mastersthesis{10.7907/J7Q1-6293, author = {Weigel, John Mitchell}, title = {Photoionization ion cylotron resonance spectroscopy: a study of three C_3H_6O isomers}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/J7Q1-6293}, url = {https://resolver.caltech.edu/CaltechTHESIS:05062010-110530214}, abstract = {Photoionization ion cyclotron resonance (pi-icr) spectroscopy is described in detail. The construction and use of rare gas resonance line lamps employing LiF windows is described, with principle emphasis on the argon resonance line lamp that produces photons of 11.62 and 11.83 eV. Calculations of the number density and single resonance signal intensity are made for primary, secondary, and tertiary ions, and the low pressure lineshape calculated for an unreactive primary ion. The ion chemistry of propanal, acetone, and propylene oxide (empirical formula C_3H_6O) is investigated using pi-icr with the argon resonance line lamp. The major reaction sequence in propanal and acetone is parent ion producing protonated parent ion, which condenses with the parent neutral to produce the proton bound dimer. This is also the reaction sequence in ethylene oxide. In propylene oxide, however, the parent ion relative abundance is esentially constant from 10^(-6) to 10^(-4) torr. The fragment ion of mass 43 is the predominant primary ion at the argon resonance lines, and reacts to form ions of mass 41, 57, and 59. Double resonance is used to determine the reaction sequence of the major ions. At 10^(-4) torr, there is less than 2% of the proton bound dimer in propylene oxide, while in acetone or propanal the proton bound dimer is the major product ion. Preliminary photolysis results on propylene oxide suggest a chain process is involved converting propylene oxide to propanal.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/T9WX-ZR66, author = {Miasek, Peter George}, title = {Trapped Ion Studies of Ion-Molecule Reactions}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/T9WX-ZR66}, url = {https://resolver.caltech.edu/CaltechTHESIS:01312018-133321152}, abstract = {Ion-molecule reactions have been studied using a novel high pressure mass spectrometer employing crossed electric and magnetic fields for ion trapping. These studies have been supplemented by ones undertaken using trapped-ion ion cyclotron resonance (ICR) spectrometry.
Reaction rate constants at low ion energies have been measured in many systems, and compare favourably with results of other studies. Correlations of measured rates with theoretical models have characterized certain features of ion-neutral collision processes. Comparisons between chemically similar systems have also provided information about these encounters.
Internal excitation of reactant ions has been shown to induce thermodynamically disallowed reactions. Evidence suggesting the participation of vibrationally excited ions reacting at different rates than their ground state counterparts is presented.
The formation and lifetimes of excited intermediates in ethylene and methanol has been investigated in detail. Relative rates of collisional stabilization of (C5H9+)* by inert gases have been determined and compared with similar processes in neutral systems. Stabilization of (C5H9+)* by ethylene itself exhibits different characteristics than those of inert gases.
The equilibrium constant of a reversible ion-molecule reaction has been measured at two temperatures and used to determine the enthalpy and entropy change for the process.
The rates of various thermoneutral proton and charge-transfer reactions have been measured using trapped ion-ion ejection ICR spectrometry. This has enabled a detailed characterization of the collisional phenomena in these systems.
The kinetic energy distribution of CH3+ arising from ionization of methyl halides has been determined using ICR spectrometry and photoionization spectroscopy. Inferences about the nature of the dissociative states are presented.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, } @phdthesis{10.7907/KJ13-G054, author = {Blint, Richard Joseph}, title = {I. Orbital Interpretation and Properties of the X¹Σ⁺, a³∏, A¹∏ and ³Σ⁺ States of BH. II. Gas Phase Reactions of Fluoromethyl Cations with Ethylene and Benzene}, school = {California Institute of Technology}, year = {1972}, doi = {10.7907/KJ13-G054}, url = {https://resolver.caltech.edu/CaltechTHESIS:10282009-093808296}, abstract = {“Ab initio” calculations have been carried out on the states of BH(χ1Σ+, a3Π, A1Π, and 3Σ+) which dissociate to the ground states of B and H. The application of the Gl method (which is a special case of the GI method) was extended to handle five- and six-electron systems, and this method along with SOGI, CI and the GVB method was used to investigate the BH states. The effect of restricting the orbitals of the wave-function to be basis functions for the irreducible representations of the spatial symmetry group leads to noncontinuous changes in the orbitals as a function of internuclear distance. And further it is noted that the removal of this restriction on the atomic wavefunction of boron leads to simple predictions of the forms of the wavefunctions, geometries of the molecules and characteristics of the potential curves for the BHN molecules. On the basis of this the potential curves for the a3Π and A1Π states are correctly predicted to have humps and the 2A1 and 2B1 states of BH2 are predicted to be bent and linear, respectively. Molecular properties for many of these wavefunctions have been calculated and correlated with changes in the orbitals as a function of internuclear distance.
Gas phase reactions and properties of fluoromethyl cations have been investigated using the techniques of ion cyclotron resonance spectroscopy (icr). Fluoride transfer reactions between substituted methyl cations are observed to be rapid and permit the determination of relative fluoride ion affinities, defined as the negative of the enthalpy change for the reaction CHNF+3-N + F- → CHNF4-N. By combining available thermochemical data and our experimental results the following order for the fluoride affinities of the methyl cations is constructed: CF+3 (256.3 kcal/mole) > CH+3 (252.0 kcal/mole) > CH2F+ (243.6 kcal/mole) > CF2H+ (242.8 kcal/mole). A measurement of the equilibrium constant for the reaction (CF2H+ + CH2F2 ⇌ CH2F+ + CF3H) between the latter two ions has permitted their relative fluoride ion affinities to be accurately determined. Fluoride ion affinities are a means of determining carbonium ion stabilities.
With the general goal of understanding reactions involving electrophillic addition to π-systems the reactions of the fluoromethyl cations with ethylene, ethylene-d4 and benzene-d6 were investigated. The important process in each case involves addition of the fluoromethyl cation to the substrate to form a chemically activated intermediate which decomposes with loss of HF or H2. Rate constants for the reactions of the fluoromethyl cations with ethylene were determined using icr trapped ion techniques. In conjunction with ion ejection double resonance, product distributions for the reactions involving ethylene-d4 and benzene-d6 have been determined. Only in the case of the reactions of fluoromethyl cations with benzene-d6 is the possibility of a distinctive reaction mechanism revealed from the isotopic product distributions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Goddard, William A., III}, } @mastersthesis{10.7907/CNW1-W685, author = {Wyatt, Robert Howard}, title = {Acidity, basicity, and ion-molecule reactions of arsine in the gas phase by ion cyclotron resonance spectroscopy}, school = {California Institute of Technology}, year = {1971}, doi = {10.7907/CNW1-W685}, url = {https://resolver.caltech.edu/CaltechTHESIS:04082010-073342301}, abstract = {
The ion-molecule reactions of arsine, both pure and in binary mixtures with several other molecules, have been investigated by ion cyclotron resonance spectroscopy. Reaction pathways, product distributions, and rate constants have been determined for the ion-molecule reactions for both positive and, to a lesser extent, negative ions. Arsine fragment ions condense with neutral AsH_3 to generate product ions containing two and, on further reaction, three atoms of arsenic. In the process of condensation, one or two molecules of H_2 are expelled. The formation of AsH_4^+ occurs from AsH_3^+ which does not undergo condensation reactions to any significant extent. Where possible, thermochemical data have been determined, including the gas phase acidity, PA(AsH_2^-) = 356 ± 6 kcal/mole, and basicity, PA(AsH_3) = 175 ± 5 kcal/mole, of AsH_3. Observation of gas phase nucleophilic displacement reactions involving AsH_3 as a nucleophile have allowed limits to be placed on the basicity of AsH_3 toward a soft acid, CH_3^+. The implications of these results are discussed and the ion-molecule reactions of AsH_3 are compared with those of other hydrides.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Beauchamp, Jesse L.}, }