NONLINEAR RAMAN-SPECTROSCOPY OF GROUND-STATE INTERMOLECULAR VIBRATIONS IN BENZENE COMPLEXES

We report the use of mass-selective, ionization-detected stimulated Raman spectroscopies in the study of ground-state intermolecular vibrational resonances in van der Waals complexes. Results are reported for one-to-one complexes of benzene isotopomers with Ar, Kr, and N2. For these species a single Raman band is observed at 33.4, 35.2, and 37.2 cm-1, respectively. All of these bands exhibit rotational contours that are several cm-1 in width and without a dominant q(Q) branch. They also exhibit polarization ratios indicative of nontotally symmetric vibrational transitions. They are shown to correlate with S1 vibrational intervals of slightly lower frequency. And, they exhibit red shifts of 2-3 cm-1 upon perdeuteration of the benzene moiety. The bands are assigned as transitions involving the van der Waals bending mode in each of the species and are most likely fundamentals of the bend.