A Theoretical Study of Dynamics at the Transition State of Gas Phase Chemical Reactions

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This research, funded by the NSF Theoretical and Computational Chemistry Program, treats two topics in the theory of state-to-state reaction dynamics. First, hydrogen atom exchange in heavy-light-heavy-atom systems is treated by quantum or semi-classical (phase space) dynamics. Second, scattering resonances will be computed by Fourier analysis of high energy quantum wavepackets evolving in the transition state region. A complex gas phase reaction consists of many elementary steps such as O+HCl = OH+Cl occurring sequentially or in parallel. The first research topic is the development of mathematical methods for predicting the rate of such an elementary reaction, in particular, one involving the transfer of a hydrogen atom from one heavy atom to another. The theory treats the dependence of the reaction rate upon the initial relative translational energy of the reactants and the vibrational and rotational quantum states of the reactants and products. In the course of a chemical reaction the molecular system usually passes through a high energy configuration known as the transition state. The second research topic attempts to follow the behavior of a molecular system which starts out in the transition state region. One way to prepare molecules in this initial condition in the laboratory is to first generate a stable negative complex ion having (approximately) the appropriate geometry, and then suddenly remove one electron by laser excitation (photodetachment). One goal of this research project is to develop the theory of these photodetachment experiments.