Quantum consideration of electron transfer solvent control

The elementary act of the electron transfer process is considered within th e quantum spin-boson model. The expression for the coordinate dependent rea ction flux correct to the second order in the intercenter coupling is obtai ned. It is shown that in the classical bath limit the flux is localized in a narrow nonadiabatic region in the vicinity of the crossing point of the p otential surfaces. Thus, the well-known point-transition model describing s olvent dynamical effect in the electron transfer kinetics is justified in t his limit. The analysis of the Markovian kinetic equations for a quantum tw o-stage electron system coupled to a classical bath used by a number of aut hors for the derivation of the point-transition model is performed. It is d emonstrated that this approach is often inappropriate for the description o f the electron transfer process. Here we show that these equations may lead to unphysical predictions such as negative reaction rate and flux. (C) 199 9 American Institute of Physics. [S0021-9606(99)51529-8].