Choice of the reaction coordinate in electron-transfer reactions in solution

Abstract

The electrochemical reduction of methyl chloride in water to give methyl radical and chloride anion has been studied by the Monte Carlo method. The carbon–chlorine distance (d_C–Cl) has been chosen to define the reaction coordinate, and a standard statistical perturbation theory has been used to obtain the Helmholtz energy change between the dividing surfaces defined by each particular value of d_C–Cl. The corresponding transition state, in the sense of the variational transition-state theory, has been located and analysed. The results have been compared with those obtained as a function of the reaction coordinate ΔE in a previous work, defined as the difference between the diabatic energy hypersurfaces for each configuration of the system. We conclude that the non-geometrical parameter, ΔE, is the best choice for the reaction coordinate.