CaltechAUTHORS: Article
https://feeds.library.caltech.edu/people/Willberg-D-M/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenMon, 14 Oct 2024 13:43:59 -0700Real-time probing of reactions in clusters
https://resolver.caltech.edu/CaltechAUTHORS:BREjcp90a
Year: 1990
DOI: 10.1063/1.458384
In this Communication we report our first study of real-time reaction dynamics in finite size clusters. The reaction is of the type AH + Sn, where the proton transfer (bimolecular) dynamics is examined as the acid AH is solvated with different number of molecules, n = 1,2,... etc. This is in continuation of out effort to study reaction dynamics in real-time [1], but now extending the scope of the previous collisionless (solvent free) condition to a range where condensed phase effects can play a role. Of particular interest to us is the condition at which solvation induces vibrational relaxation and modifies IVR. Real-time studies of reactions in clusters offer great opportunities for obtaining the rates directly [2] and for examining these solvation processes under controlled conditions in molecular beams. Such stepwise solvation by beam methods has been advanced for a variety of systems spanning small molecules [3], large molecules [4], hydrogen-bonded systems [5], and electrons [6].https://resolver.caltech.edu/CaltechAUTHORS:BREjcp90aDirect observation of the picosecond dynamics of I_2-Ar fragmentation
https://resolver.caltech.edu/CaltechAUTHORS:20120424-142558756
Year: 1990
DOI: 10.1063/1.459207
Picosecond real‐time observations of the dynamics of I_2–Ar fragmentation are reported. The state‐to‐state rates, k(ν^i,,ν^f,), are directly measured and related to the homogeneous broadening of the initial state, and to product state distributions in the exit channel. Comparisons with different theories of vibrational (and electronic) predissociation are made.https://resolver.caltech.edu/CaltechAUTHORS:20120424-142558756Rotational constants of vibrationally excited iodine from purely rotational coherence observed in pump-probe experiments
https://resolver.caltech.edu/CaltechAUTHORS:20160830-102557022
Year: 1991
DOI: 10.1021/j100172a010
Pump-probe laser-induced fluorescence techniques are used to determine the rotational constants of vibrationally excited iodine, cooled by supersonic beam expansions. For comparison, it is shown that the results obtained from real time (purely rotational coherence) are in excellent agreement with literature values for the v' = 12-23 of the B state. Results for nascent I_2 (v' = 22), from the predissociation of I_2Ne (v' = 23), are also reported.https://resolver.caltech.edu/CaltechAUTHORS:20160830-102557022Real-time dynamics of clusters. I. I_2X_n(n=1)
https://resolver.caltech.edu/CaltechAUTHORS:20120330-073046238
Year: 1992
DOI: 10.1063/1.462499
Vibrational predissociation of I_2X_n (X=Ne, Ar) van der Waals clusters are studied in real‐time using picosecond pump–probe (LIF) and molecular beam techniques. The state‐to‐state rates of vibrational predissociation are measured for specific vibrational levels v′_i by monitoring the rise of nascent I_2. Here, we report our study of I_2X(B,v′_i)k(v '_i,v′_f) →I_2(B,v′_f)+X. For I_2Ne, the values of τ=k^(−1)(v'_i,v′_f) decrease nonlinearly from 216 ps for v'_i=13 to 53 ps for v′_i=23. For I_2Ar (B,v'_i), which undergo electronic and vibrational predissociation, the risetime of the nascent I_2 is found to be 70 ps when v′_i=18 and 77 ps when v'_i=21. A number of theoretical models for vibrational predissociation (the energy‐gap law, the momentum‐gap law, quantum and classical calculations) are compared with our experimental results in an attempt to understand the key features of the dynamics and the potential energy surface.https://resolver.caltech.edu/CaltechAUTHORS:20120330-073046238Real-time dynamics of clusters. II. I_2X_n (n=1; X=He, Ne, and H_2), picosecond fragmentation
https://resolver.caltech.edu/CaltechAUTHORS:GUTjcp92a
Year: 1992
DOI: 10.1063/1.463426
In this second paper (II) of a series, we report our picosecond time-resolved studies of the state-to-state rates of vibrational predissociation in iodine–rare gas (van der Waals) clusters. Particular focus is on the simplest system, I2He, which serves as a benchmark for theoretical modeling. Comparisons with I2Ne and I2H2 are also presented. The results from measurements made in real time are compared with those deduced from linewidth measurements, representing a rare example of a system studied by both methods under identical conditions and excited to the same quantum (v<sup>[script ']</sup><sub>i</sub>) states. The discrepancies are discussed in relation to the origin of the broadening and preparation of the state. The rates as a function of v<sup>[script ']</sup><sub>i</sub> display a nonlinear behavior which is examined in relation to the energy-gap law. The measured absolute rates and their dependence on v<sup>[script ']</sup><sub>i</sub> are compared with numerous calculations invoking classical, quantum, and semiclassical theories. In the following paper (III in this series), the cluster size of the same system, I2Xn, is increased (n=2–4) and the dynamics are studied.https://resolver.caltech.edu/CaltechAUTHORS:GUTjcp92aReal-time dynamics of clusters. III. I_2Ne_n (n=2–4), picosecond fragmentation, and evaporation
https://resolver.caltech.edu/CaltechAUTHORS:GUTjcp92b
Year: 1992
DOI: 10.1063/1.463427
In this paper (III) we report real-time studies of the picosecond dynamics of iodine in Ne clusters I<sup>*</sup><sub>2</sub>Nen(n = 2–4) --> I<sup>*</sup><sub>2</sub> + nNe. The results are discussed in relation to vibrational predissociation (VP), basic to the I2X systems, and to the onset of intramolecular vibrational-energy redistribution (IVR). The latter process, which is a precursor for the evaporation of the host atoms or for further fragmentation, is found to be increasingly effective as the cluster size increases; low-energy van der Waals modes act as the accepting (bath) modes. The reaction dynamics for I2Ne2 are examined and quantitatively compared to a simple model which describes the dynamics as consecutive bond breaking. On this basis, it is concluded that the onset of energy redistribution is observed in I2Ne2. Comparison of I2Ne and I2Ne2 to larger clusters (n=3,4) is accomplished by introducing an overall effective reaction rate. From measurements of the rates and their dependence on v<sup>[script ']</sup><sub>i</sub>, the initial quantum number of the I2 stretch, we are able to examine the dynamics of direct fragmentation and evaporation, and compare with theory.https://resolver.caltech.edu/CaltechAUTHORS:GUTjcp92bA simple description of vibrational predissociation by a full-collision approach
https://resolver.caltech.edu/CaltechAUTHORS:20160829-150314802
Year: 1993
DOI: 10.1016/0009-2614(93)85109-2
A simple theoretical model is described for vibrational predissociation. The model, which is based on a full-collision approach, predicts the dependence of the rates on the initial quantum number and focuses on the importance of the repulsive force along the van der Waals coordinate. Picosecond state-to-state rates are measured for I_2He (and I_2Ne) in different quantum numbers of the I_2 and I_2He coordinates, and the results are compared with the results of the model.https://resolver.caltech.edu/CaltechAUTHORS:20160829-150314802Solvation Ultrafast Dynamics of Reactions. 8. Acid-Base Reactions in Finite-Sized Clusters of Naphthol in Ammonia, Water, and Piperidine
https://resolver.caltech.edu/CaltechAUTHORS:20160825-105753860
Year: 1995
DOI: 10.1021/j100019a027
In this contribution, studies of the dynamics of proton-transfer reactions in solvent cages are presented, building
on earlier work [Breen, J. J.; et al. J. Chem. Phys. 1990, 92, 805. Kim, S. K.; et al. Chem. Phys. Lett. 1994,
228, 369]. The acid-base system studied in a molecular beam is 1-naphthol as a solute and ammonia, piperidine, or water as the solvent, with the number of solvent molecules (n) varying. The rates and threshold
for proton transfer have been found to be critically dependent on the number and type of solvent molecules:
n = 2 for piperidine and n = 3 for ammonia; no proton transfer was observed for water up ton = 21. With
subpicosecond time resolution, we observe a biexponential transient for the n = 3 cluster with ammonia.
From these observations and the high accuracy of the fits, we provide the rate of the proton transfer at short
times and the solvent reorganization at longer times. From studies of the effect of the total energy, the
isotope substitution, and the number and type of solvent molecules, we discuss the nature of the transfer and
the interplay between the local structure of the base solvent and the dynamics. The effective shape of the
potential energy surface is discussed by considering the anharmonicity of the reactant states and the Coulombic
interaction of ion-pair product states. Tunneling is related to the nature of the potential and to measurements
specific to the isotope effect and energy dependence. Finally, we discuss a simple model for the reaction in
finite-sized clusters, which takes into account the proton affinity and the dielectric shielding of the solvent
introduced by the local structure.https://resolver.caltech.edu/CaltechAUTHORS:20160825-105753860Electrohydraulic destruction of hazardous wastes
https://resolver.caltech.edu/CaltechAUTHORS:20150821-083013604
Year: 1996
Much research has been devoted to developing advanced oxidation technologies for destroying hazardous chemical wastes. The fundamental chemistry behind these processes has been studied extensively and is reasonably well understood; however, their scale-up from the bench to the pilot plant or field test is not a trivial exercise. Major engineering challenges exist in designing nonthermal industrial oxidation technologies that are cost-effective, robust, and versatile. One possible approach is to use existing technologies that have proven to be successful in industrial applications. The electrohydraulic discharge (EHD) method is a non-thermal process based on pulsed-power technology. EHD injects energy into an aqueous solution through a plasma channel formed by a high-current/high-voltage electrical discharge between two submersed electrodes. The paper describes system design, degradation experiments to elucidate the oxidation kinetics, EHD-ozone experiments, and energy efficiency.https://resolver.caltech.edu/CaltechAUTHORS:20150821-083013604Degradation of 4-Chlorophenol, 3,4-Dichloroaniline, and 2,4,6-Trinitrotoluene in an Electrohydraulic Discharge Reactor
https://resolver.caltech.edu/CaltechAUTHORS:20150810-152944999
Year: 1996
DOI: 10.1021/es950850s
An electrohydraulic discharge (EHD) process for the treatment of hazardous chemical wastes in water has been developed. The liquid waste in a 4-L EHD reactor is directly exposed to high-energy pulsed electrical discharges between two submerged electrodes. The high-temperature (>14 000 K) plasma channel created by an EHD emits ultraviolet radiation and produces an intense shockwave as it expands against the surrounding water. The oxidative degradation of 4-chlorophenol (4-CP), 3,4-dichloroaniline (3,4-DCA), and 2,4,6-trinitrotoluene (TNT) in an EHD reactor was explored. The initial rates of degradation for the three substrates are described by dC/dN = −k_1C_i − k_0, where dC/dN is the change in concentration per discharge; Ci is the initial substrate concentration; k_0 is the zero-order term that accounts for direct photolysis; and k1 is the first-order term that accounts for oxidation in the plasma channel region. For 4-CP in the 4-L reactor, the values of these two rate constants are k_0 = 0.73 ± 0.08 μM discharge^(-1) and k_1 = (9.4 ± 1.4) × 10^(-4) discharge^(-1). For a 200 μM 4-CP solution, this corresponds to an overall intrinsic zero-order rate constant of 0.022 M s^(-1) and a G value of 4.45 × 10^(-3). Ozone increases the rate and extent of degradation of the substrates in the EHD reactor. Combined EHD/ozone treatment of a 160 μM TNT solution resulted in the complete degradation of TNT and a 34% reduction of the total organic carbon (TOC). The intrinsic initial rate constant of TNT degradation was 0.024 M s^(-1). The results of these experiments demonstrate the potential application of the EHD process for the treatment of hazardous wastes.https://resolver.caltech.edu/CaltechAUTHORS:20150810-152944999Oxidative Degradation of 2,4,6-Trinitrotoluene by Ozone in an Electrohydraulic Discharge Reactor
https://resolver.caltech.edu/CaltechAUTHORS:20150807-112624545
Year: 1998
DOI: 10.1021/es980052c
The electrohydraulic discharge process in the presence of ozone has been used to investigate the rapid degradation and mineralization of aqueous 2,4,6-trinitrotoluene (TNT) solutions that were directly exposed to high-energy electrical discharges between two submerged electrodes. The 165 μM solutions of TNT were completely (>90%) mineralized over the course of 300 electrical discharges of 7 kJ each. The kinetics of TNT degradation were investigated as a function of the aqueous-phase ozone concentration, pH, discharge energy, and electrode gap length. The rate of TNT degradation increases with an increase in aqueous-phase ozone concentration of up to 150 μM, an increase in pH from 3.0 to 7.9, an increase in discharge energy from 5.5 to 9 kJ, and a decrease in the electrode gap length from 10 to 6 mm. The rapid rates of mineralization (e.g. 12 ms) are attributed to the action of UV light in the reactor chamber on O_3 to produce a high flux of hydroxyl radicals per discharge (1 μM discharge^(-1)). The primary reaction intermediates were 2,4,6-trinitrobenzaldehyde and trinitrobenzene.https://resolver.caltech.edu/CaltechAUTHORS:20150807-112624545