Solvation and dielectric dispersion in optical electron transfer

The effect of dielectric dispersion of the solvent on the energetics of optical electron transfer is determined quantitatively by variations of the free energy of solvation of the species being photoionized. The solvation free energy varies because the solvent polarizability in the inner-sphere region of the photon absorbing species changes with photon energy on account of dispersion. The solvation free energy is computed for a varying polarizability of the solvent in the inner-sphere region and a fixed nuclear configuration of the solvent. The following interaction energies are considered: charge–induced dipole, dipole–induced dipole, induced dipole–induced dipole, formation of induced dipoles, solute–solvent London dispersion, solvent–solvent London dispersion, and solute–solvent and solvent–solvent Born repulsion. The change of solvation free energy in aqueous solution is computed in the 7 to 11 eV range from data on the refractive index of water obtained by reflectance spectroscopy. The theory accounts quantitatively for the effect of dispersion on photoelectron emission by aqueous solutions of anions, cations, and molecules.