Ultrafast control and dynamics of chemical reactions

Citation

Potter, Earl Douglas (1993) Ultrafast control and dynamics of chemical reactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/k9hx-hh19. https://resolver.caltech.edu/CaltechETD:etd-04042008-113817

Abstract

This thesis presents four distinct applications of ultrafast laser spectroscopy. Unimolecular photodissociation was one of the early applications of this technique and proved to be invaluable in furthering the understanding of unimolecular dissociation mechanisms. As such, the photodissociation of ketene represents one of the two systems where micro-canonical, state-to-state reaction rates, have been measured. Clocking of bimolecular reactions, while still in its infancy, provides a means of measuring the rate at which an elementary reaction actually occurs--isolated from other molecules. The rate at which the bimolecular reaction of bromine atoms with molecular iodine to form iodine monobromide has been measured at two collision energies. An area where ultrafast techniques are just now seeing application, is control of chemical reactions. This thesis illustrates an initial study, albeit limited, of how ultrashort light pulses can be used to "control" the outcome of a chemical reaction. The experiments here show how the natural wave-packet motion of the initially prepared B state iodine can be used to "control" whether or not xenon iodide is formed even when the necessary photons are available. Finally, cluster science is becoming a mature field within physical chemistry, but one of the goals of such work has been to make a connection between gas-phase studies and condensed-phase work. Small clusters, those not large enough to bridge this gap, have proven sufficiently interesting to monopolize the efforts of many groups. Again in a limited way, we have begun to study large clusters in the hope that these systems will truly show characteristics that are somehow intermediate to the gas-phase and condensed-phase characteristics. A dissociating iodine molecule surrounded by many argon atoms encounters an environment that significantly alters the time scales and overall mechanism for separation of the two iodine atoms.

Work done under the direction of Professor Ahmed H. Zewail.

Thesis Files