Nonlocal Effects and the Overscreening Effect in the Kinetics of Heterogeneous Charge Transfer Reactions

Abstract

The effect of the spatial dispersion of the solvent on kinetic parameters of heterogeneous charge transfer reactions is considered by using the (Cp)2Co+/(Cp)2Co (Cp—cyclopentadienyl) reaction as the example and allowing for the effects of overscreening and field penetration into the metal. The calculations are based on an exactly solvable sharp-boundary model of the metal/polar solvent interface. Parameters of the analytical expression used for the dielectric function e(k) of the solvent are selected so as to reproduce the results of calculations of the e(k) function obtained by a molecular dynamics method. Acetonitrile and dimethyl sulfoxide are considered as the solvents. The reorganization free energy infinitely away from the electrode is calculated using a model of a smeared Born sphere for the reactant ion. The smearing parameters are selected so as to obtain the electrostatic part of the solvation free energy of the ion in the solvent bulk. A method of an effective Born sphere for the ion is suggested and substantiated. The method is intended for the description of reorganization and activation free energies near the electrode surface. The reorganization and activation free energies are shown to reduce with the reactant approaching the electrode. Numerical values of these energies are greater than those computed in the classic limit with the Marcus formula and nicely conform to the estimates obtained from experimental data.