Theories of chemical reactions: the orbiting transition state for linear molecules, classical dynamics of association and dissociation in collinear reactions

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Texas Tech University

In this dissertation we examine two topics in the theory of chemical reactions. The first involves statistical theory of reaction dynamics, particularly that of the orbiting transition state (i.e., phase space theory). The second involves a classical dynamics study of a simple system. In Part 1 we examine two approximations to the orbiting transition state sum of states for systems containing linear molecules. The first is a low angular momentum approximation which was originally introduced by Klots and shown by him to be exact in the limit of zero angular momentum. The second is an "integral" approximation in that it is designed to work well when the sum of states is integrated over a large range of angular momenta, a situation in which the Klots approximation usually fails. Part 2 reports a study of the classical dynamics of collinear collision induced dissociation and association at energies slightly above the diatom dissociation threshold. The method of Andrews and Chesnavich is used to define the banding of the reagents' phase space into reactive, nonreactive, dissociative, associative and nonassociative regions for fixed total energy. In the bound region of the reagent diatom phase space, two dynamically distinct reactive bands, surrounded by companion dissociative bands, are embedded within a nonreactive region, while in the nonbound region of the reagent's phase space, association bands are seen that are simple extensions across the dissociation threshold of the reactive and nonreactive bands. The dynamics also varies smoothly across the dissociation threshold. No evidence was found for the existence of periodic or "trapped" trajectories at the energies of this study.

Chemical reactions, Collisions (Nuclear physics), Molecular theory