Near-contact adiabatic suppression of electron transfer in the inverted region

Abstract

A few theories of activated electron transfer in inverted Marcus region are used for bridging the non-adiabatic, solvent controlled and deeply adiabatic transfer. The simple analytical interpolation between dynamic and stochastic theories provides a continuous description of the electron transfer rate at any non-adiabatic coupling between the diabatic states. When coupling increases with shortening of inter-particle distance the pre-exponent of the Arrhenius transfer rate first increases being quadratic in coupling, then levels off approaching the “dynamic solvent effect” (DSE) region and finally is cut off exponentially due to adiabaticity of the transfer. These changes affect significantly the spatial dependence of the transfer rate near the contact provided the coupling there is strong. The rate tends to zero at contact distance being strongly suppressed nearby adiabatically. It is much smaller then the perturbation (golden rule) and even DSE results. The latter is actually unattainable anywhere if contact tunneling is really strong. The transfer rate is a bell-shaped curve adiabatic and non-adiabatic on the opposite sides and sensitive to the friction (DSE damping) only in between, near the maximum.