The Effect of Solvent Fluctuations in Electron Transfer Processes

Abstract

The homogeneous outer sphere electron transfer reactions in solution occur at a rate that is noticeably lower than the diffusion rate. This peculiar behaviour has been explained¹ through a three-step mechanism: formation of a precursor complex from the separated reactants, actual electron transfer within this complex to form a successor complex and dissociation of the latter complex into separated products. The reaction rate is usually controlled by the electron transfer step, this step being governed by the Franck-Condon principle. This principle is embodied in classical electron transfer theories using an activated-complex formalism in which the electron transfer cccurs at the intersection of two potential energy surfaces, one for the reactants and the other for the products. This implies that the second step necessarily involves the reorganization of the solvent before and after the electron transfer itself is produced. So, it is obvious that solvent must play an essential role in the rate of electron transfer reactions in solution.