The role of collective solvent coordinates and nonequilibrium solvation incharge-transfer reactions

In this article we discuss how the solvent energy-gap reaction coordinate a rising in weak-overlap charge-transfer theory may be generalized to include nonequilibrium solvation effects in variational transition state theory (V TST) for arbitrary reactions of neutral or charged species. The discussion also indicates how the parameters of weak-overlap charge-transfer theory ma y be related to the potential energy surface of a reaction and the potentia l of mean force. This synthesis of aspects of weak-overlap charge-transfer theory and variational transition state theory provides a clearer picture o f the usefulness and limitations of the energy-gap coordinate in Marcus the ory or in more general contexts. Furthermore, it furnishes a new view of th e role of solvent coordinates in electronically adiabatic reactions. As an example, we show how VTST provides a way to treat solute vibrational coordi nates and collective solvation coordinates in a comparable way in the compu tational modeling of aqeuous proton-transfer reactions including quantum me chanical vibrations and multidimensional tunneling effects.