Quantum theory of solvent effects on electronic spectra: Predictions of the exact solution of the mean spherical model

A microscopic quantum statistical mechanical theory for the solvent modification of the electronic spectra of nonpolar solutes is developed. Attention is focused on the solute frequency shift as a function of molecular parameters, solvent dielectric constant, and density. Comparison of the predictions of the quantum theory and dielectric continuum models (Onsager-Böttcher and Wertheim) based on the macroscopic reaction field picture are made. Significant differences are found which indicate the importance of solvent structure and nonzero frequency effects absent in the dielectric models. The theory is also applied to several aromatic hydrocarbon molecules in dilute solution with emphasis on the isothermal density dependence of the electronic frequency shift. Generalization of the quantum theory to treat polar solutes is briefly outlined.