Symmetry selection rules for reaction mechanisms

The quantum description of a potential energy surface is shown, in the context of simple transition state theory, to lead naturally to a two-stage symmetry selection procedure for reaction mechanisms which is philosophically consistent with the generalized selection rule approach recently developed for spectroscopic processes. The first stage is the determination of those reaction mechanisms that are strictly allowed by symmetry, and is related to those approaches in which spatial symmetry is used to eliminate certain transition state symmetries. The second stage, which addresses the question of the relative probabilities of the symmetry-allowed mechanisms, is related to orbital symmetry approaches to reaction mechanisms.