Anharmonic Vibrational Coupling
The goal is to observe vibrational coupling between the low and high frequency vibrational modes in various solvents. Femtosecond stimulated Raman spectroscopy (FSRS) has a unique ability to impart and probe coherent vibrational motion. We have been developing this capability further, in order to initiate low-frequency vibrational coherence via impulsive excitation and then probe its effect on other vibrational modes of interest. The technique could potentially measure anharmonic coupling between vibrational modes as well as non-linear polarizability coupling between normal modes. Since anharmonic coupling is the primary means by which vibrations exchange energy with each other (for instance, how an excited C-H stretching mode might relax to produce excited C=C and C-C stretches), this method could be used to study intramolecular vibrational relaxation (IVR, a.k.a. vibrational energy redistribution or VER) and vibrational cooling.