QUANTUM EFFECTS IN ADIABATIC ELECTROCHEMICAL ELECTRON-TRANSFER REACTIONS

The role of nuclear tunneling in adiabatic electrochemical electron-tr ansfer reactions is studied by applying the WKB approximation and the Quantum Kramers Theory to the ground-state potential energy surface ca lculated from an extended Anderson-Newns Hamiltonian. Reorganization o f both solvent and ligand modes is considered. In the limit of vanishi ng electronic coupling analytical formulas are obtained for the temper ature dependence of the activation parameters, which are valid over a practically unlimited temperature range. In the limit of high temperat ure, they are shown to be identical to expressions derived from the no n-adiabatic Levich-Dogonadze theory. The effect of friction and non-va nishing electronic coupling are studied and both are found to suppress the relative contribution of the nuclear tunneling to the overall rea ction rate. (C) 1997 Published by Elsevier Science B.V.