A simple model for electrochemical ion transfer reactions, based on an
extended Anderson-Newns model [W. Schmickler, Chem. Phys. Lett. 237 (
1995) 152], is treated within the framework of the multidimensional Kr
amers theory to calculate ion transfer rates. It is shown that for uni
valent ion transfer, the rate constant may be substantially influenced
by a partial charge transfer during the rate-determining step of the
adsorption process, even though the activation barrier is mainly deter
mined by the separation from the metal surface. In the limit of strong
ly overdamped solvent dynamics, however, the energetically favourable
adiabatic electron exchange with the electrode is suppressed and the e
ffective reaction coordinate is again one-dimensional, and given by th
e separation from the surface.