Quantum effects in adiabatic electrochemical electron-transfer reactions

The role of nuclear tunneling in adiabatic electrochemical electron-transfer reactions is studied by applying the WKB approximation and the Quantum Kramers Theory to the ground-state potential energy surface calculated from an extended Anderson-Newns Hamiltonian. Reorganization of both solvent and ligand modes is considered. In the limit of vanishing electronic coupling analytical formulas are obtained for the temperature dependence of the activation parameters, which are valid over a practically unlimited temperature range. In the limit of high temperature, they are shown to be identical to expressions derived from the non-adiabatic Levich-Dogonadze theory. The effect of friction and non-vanishing electronic coupling are studied and both are found to suppress the relative contribution of the nuclear tunneling to the overall reaction rate. (C) 1997 Published by Elsevier Science B.V.