Time and neighbor interaction in resonance Raman spectroscopy

We study systems in which the resonance Raman process is fast due to the requirement for phonon involvement in the absorption. The resonance enhancement is found to track the isolated molecule, or vapor phase, absorption since the molecule does not have time to exchange energy with its neighbors. This corroborates with studies of pre-resonance, where Heisenberg’s uncertainty principle enforces a rapid process, but differs from resonance on electronically allowed transitions, where the resonance allows a relatively prolonged interaction. High resolution excitation spectroscopy reveals large gains and narrow features usually associated with the isolated molecule. Vibration energies shift as the resonance is approached and the excited state vibration levels are probed. Several multiplets and overtone modes are enhanced along with the strongly coupled ring-breathing mode in aromatic molecules.