Intermolecular vibrational resonance coupling: Intensity borrowing in polarized Raman spectroscopy

The effects of solvent‐solute interactions on polarized and depolarized Raman intensity are investigated using perturbation theory, accounting for correlations in the relative orientations of the interacting transition dipoles. Two mechanisms for intensity borrowing are considered: interaction of the vibrational transition moments in the ground electronic states, and coupling of the electronic transition moments responsible for resonance Raman enhancement. The first type of interaction is shown to lead to measurable frequency shifts and depolarization ratio changes for two coupled vibrations which are infrared active and close in frequency. The second mechanism, not dependent on vibrational resonance, leads to perturbations of the depolarization ratio in resonance Raman, but not to vibrational frequency shifts.