The Relation Between the Barriers for Thermal and Optical Electron Transfer Reactions in Solution

Abstract

The relation between the energy of the intervalence (or metal-to-metal charge-transfer) transition in mixed-valence systems and the magnitude of the barrier to thermally activated electron transfer is described. We note that, contrary to what has frequently been assumed, the relation is in terms of free energies rather than internal energies or enthalpies. It is also shown, from plots of the enthalpies of the reactants and products versus the reaction coordinate, that negative activation enthalpies are a natural consequence when the standard enthalpy change for the reaction is sufficiently negative.