Adiabatic electrochemical electron-transfer reactions involving frequency changes of inner-sphere modes

A Hamiltonian model is formulated for electrochemical electron-transfer reactions involving frequency changes of the inner-sphere modes. The adiabatic free energy surface is calculated and it is shown that this nonlinear coupling leads to a transfer coefficient different from 1/2, and that the transfer coefficient can no longer be identified with the electron occupation probability in the transition state saddle point, as in the linear coupling case. (C) 1999 Elsevier Science S.A. All rights reserved.