A FREQUENCY-RESOLVED CAVITY MODEL (FRCM) FOR TREATING EQUILIBRIUM ANDNONEQUILIBRIUM SOLVATION ENERGIES

A refined continuum medium model, denoted as the 'frequency-resolved c avity model' (FRCM), for describing solvation effects of electrically charged solutes in polar solvents is considered. The principal distinc tion between the commonly accepted Born-Kirkwood-Onsager model and the FRCM treatment is that in the latter case the medium polarization fie ld induced by the solute charge distribution is subdivided into inerti al and inertialess components associated with different cavities. The inertialess field, arising from solvent electronic polarization modes, involves an inner cavity confined inside a larger one, which establis hes the boundary for inertial polarization modes corresponding to coll ective orientational and translational motions of solvent molecules ou tside both cavities. The model is formulated so as to be applicable to complicated chemical solutes, with no symmetry limitations imposed on the shape of their cavities and charge distributions. In introducing two cavities, we find that a single extra parameter in the refined mod el, chosen to control the distinct sizes of the cavities, is capable o f providing the necessary additional flexibility to the FRCM parametri zation scheme. By this means one can redistribute inertial and inertia less contributions to equilibrium solvation energies in a way which is consistent with existing experimental data for both equilibrium solva tion energy solvent reorganization energy. (C) 1998 Elsevier Science B .V. All rights reserved.