MOLECULAR SOLVENT-DYNAMICAL EFFECTS ON ACTIVATED ELECTRON-TRANSFER KINETICS - HOW IMPORTANT IS SOLVENT FRICTION

The likely extent of retardation exerted by solvent friction upon the rates of activated electron-transfer (ET) processes is explored and ev aluated with reference to some extant solvent-dependent data for metal locene ET self exchanges. Barrier-crossing frequencies extracted from the experimental kinetic and barrier data for suitably adiabatic react ions are compared with solvent inertial frequencies (i.e. the zero-fri ction limit) as estimated from currently available analytic expression s. The additional extent of rate retardation seen in passing from low- friction to ostensibly strongly overdamped solvents, as deduced in thi s manner, is seen to be muted substantially in comparison with the pre dictions of conventional Debye-continuum approaches, although followin g a solvent functionality that is nevertheless roughly in accord with the latter. The likely importance of more rapid dynamics associated wi th short-range (molecular) solvation is addressed in the light of thes e findings.