Quantum consideration of electron transfer solvent control

The elementary act of the electron transfer process is considered within the quantum spin-boson model. The expression for the coordinate dependent reaction flux correct to the second order in the intercenter coupling is obtained. 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 potential surfaces. Thus, the well-known point-transition model describing solvent dynamical effect in the electron transfer kinetics is justified in this limit. The analysis of the Markovian kinetic equations for a quantum two-stage electron system coupled to a classical bath used by a number of authors for the derivation of the point-transition model is performed. It is demonstrated that this approach is often inappropriate for the description of the electron transfer process. Here we show that these equations may lead to unphysical predictions such as negative reaction rate and flux. (C) 1999 American Institute of Physics. [S0021-9606(99)51529-8].