|
|
|
|
M. Tachiya, and M. Hilczer
[Ultrafast Reaction Dynamics and Solvent Effects (AIP CONF. PROC. 298), pp.447-459, 1994]
The Marcus equation of the electron transfer rate is generalized to the form which is applicable to molecular models of the solvent. The rate constant is expressed in terms of the function ø(DeltaV) which describes the distribution of the electrostatic potential difference DeltaV between donor and acceptor sites, produced by the surrounding fluctuating polar solvent molecules. This expression clearly shows that the functional dependence of the rate constant on the free energy change of reaction (the so-called energy gap law) reflects the potential difference distribution ø(DeltaV). The new expression is applicable not only to the dielectric continuum model but also to any molecular model of the solvent. It reduces to the well-known Marcus equation, if it is combined with the potential difference distribution calculated on the basis of the dielectric continuum model. In order to improve the Marcus equation the potential difference distribution is calculated on the basis of a realistic molecular model of the solvent by using molecular dynamics simulations (Fig.1). The effect of donor and acceptor diffusion on the electron transfer rate is also investigated.
