Theory of simple electron transfer reactions in solution

Abstract

This paper reports the analysis of an electron transfer, oxidation-reduction reaction system. The model electron transfer system consists of a dielectric continuum solvent in which charged electron donor and acceptor reactants are dissolved. The reactants in this model behave as hard sphere entities with internal degrees of vibronic freedom; however, the hard sphere character is important only in connexion with the dynamics of the reactant's encounter during the course of the electron transfer. This model, therefore, apart from the internal vibronic degrees of freedom, is the same as that examined by Levich and Dogonadze. Our analysis of the model system employs the Yamamoto reaction rate theory to obtain electron transfer rate constant expressions. These derived theoretical rate constants are general; they apply to all reactions from those classified as chemically adiabatic to the non-adiabatic cases. The effects of internal vibronic degrees of freedom appear in the rate constant expressions both as additional terms in the energy exponent and in the pre-exponential factor. This manifestation of vibronic contributions is expressed in the pre-exponential factor as a power series in the temperature. The introduction of this additional dynamical dependence on internal degrees of freedom prepares the way to the theoretical consideration of more complicated electron transfer systems.