A viscoelastic continuum model of nonpolar solvation. III. Electron solvation and nonlinear coupling effects

Abstract

The viscoelastic (VE) continuum model of solvation developed in the first paper of this series [J. Phys. Chem. A 102, 17 (1998)] is applied to solvation of the electron in water and is compared to the computer simulations of Rossky and co-workers. The theory correctly predicts both the inertial and diffusive solvation times for both injected electrons and electrons excited to the p state. These times are associated with the speed of phonon propagation and the rate of shear relaxation respectively. The ability of the VE model to predict the inertial solvation time shows that continuum models are a valuable first approximation, even at very short times. The full solvation response function, the time-dependent cavity shape and the effect of deuteration are also all reproduced accurately for solvation of the p state. The effect of a shape change in the excited state of the electron is compared to the effect of a size change. A shape change produces a low amplitude, picosecond tail in the solvation response function, which is not present with a purely spherical size change. The theory is extended to include quadratic terms in the solvation difference potential. This nonlinearity accounts for the largest differences between the solvation response function in the ground and excited states of the electron. All the major features seen in the simulations can be accounted for by mechanical relaxation of the solvent. At present, there is no compelling indication of a significant role for dielectric relaxation, although the issue merits further investigation.