Unimolecular reaction rate theory for highly flexible transition states. 2. Conventional coordinate formulas for the various possible fragment combinations: miscellaneous topics

Abstract

A method for using conventional coordinates in the implementation of RRKM theory for unimolecular dissociations was described in part 1 of this series, for the case where both fragment molecules are nonlinear. The corresponding formalism for all possible types of fragments, atomic, linear, and nonlinear fragments and their combinations, is presented here. Also discussed analytically is the tendency, in a unimolecular dissociation, for the position of the transition state to move to shorter fragment-fragment separation distances with increasing total energy E. This tendency has marked consequences, including increasing deviation of rate constants from those of phase space theory with increasing E and, in the case of fragment-fragment recombination, a corresponding tendency for high-pressure rate constants to decrease with increasing temperature. Two other topics considered in this paper are the case of two minima in the variational calculation and the role of the repulsive potential energy curves in the unimolecular dissociations under consideration.

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