CONTROL OF ELECTRON TRANSFER RATES BY MOTIONS OF ATOMS AND MOLECULES

Abstract

Recently, measurements have been made of the temperature dependence of long distance intramolecular electron transfer reactions in molecules in which donor and acceptor groups are held at a fixed distance apart. For very highly exoergic electron transfer reactions, the rates show a remarkable independence of temperature. This temperature independence can be predicted quite precisely from the results of previous experiments which measured only the dependence of rates on free energy change. The temperature dependence can be ascribed to “nuclear tunneling” in high frequency vibrational modes which are coupled to the electron transfer reaction. While this is not surprising, the dominance of even a small coupling to high frequency modes in determining the temperature dependence is surprising. The importance of the high frequency modes is likely to be apparent in other contexts, particularly cases in which “dynamic solvent” effects occur for electron transfer reactions in highly viscous media.