Quantum theory of the electronic absorption line shape of a solvated molecule

Abstract

A quantum statistical mechanical theory of the electronic absorption line shape of a polarizable solute molecule at infinite dilution in a polarizable solvent is developed. Solute and solvent molecules are modeled as electronic two-level systems whose interactions have the transition dipole–transition dipole form. The theory predicts solvent-induced line broadening, as well as a line shift. The inhomogeneously broadened line shape corresponding to a single vibronic transition of the solute molecule is predicted to be asymmetric. The line shape falls off more slowly as the frequency is tuned from the solute absorption peak away from the solvent absorption band, than it does as the frequency is tuned toward the solvent absorption band. The results suggest that the line shape is sensitive to the local fluid structure.