Reaction dynamics on barrierless reaction surfaces. II: Microcanonical variational transition states

A previous quasiclassical trajectory investigation of a generic proton-transfer reaction [Lim and Brauman, J. Chem. Phys. 94, 7164 (1991)] suggested the existence of both the usual centrifugal barrier transition state and a ‘‘dynamic’’ nonenergetic transition state for association on a barrierless potential surface. This paper reports a microcanonical variational transition state theory investigation of the same potential surface. The dynamic transition state is found to fulfill the variational criterion of a minimum in the sum of states. Implications for ion/molecule reactions are discussed.