Implementation and limitations of the transition-state theory for ion–molecule systems with non-spherical dividing surfaces

Abstract

Some inconsistencies in the use of transition–state theory (TST) to calculate rate constants for ion-polar molecule reactions are indicated. For strongly polar molecule involving small orbital angular momenta there is, for a certain range of orbital angular momenta and orientation angles, no way to define the critical dividing surface, S*, and the notion of capture becomes meaningless. For collisions involving large orbital angular momenta S* can be defined for all orientation angles but will be spherically unsymmetrical. The surface should be chosen so that the flux normal to it is a minimum. While conventional TST versions are shown to fail, the equations are derived that ensure the minimum flux for a given S*. The iterative version of TST is formulated that makes it possible to find the optimum S*.