ON THE DIFFERENCES IN THE MAGNITUDE OF THE OBSERVED SOLVENT EFFECT IN THE KINETICS OF SIMPLE HETEROGENEOUS ELECTRON-TRANSFER REACTIONS

Solvent effects have been examined for 18 simple heterogeneous redox reactions involving one-electron oxidation of a molecule to form a monocation or one-electron reduction to form a monoanion. It is shown that the degree of dependence of the rate constant on the longitudinal relaxation time of the solvent decreases with the experimental value of the standard rate constant. This observation is discussed within the context of contemporary theory for the effect of the solvent on the pre-exponential factor for the rate constant. It is concluded that, as the importance of solvent fluctuations on the frequency of crossing the Gibbs activation energy barrier for electron transfer decreases, there is a corresponding decrease in the electron transmission coefficient.