Nonlinear Raman spectroscopy of intermolecular vibrations in benzene-(water)n clusters

We report species-selective spectra of intermolecular vibrational transitions in benzene-(water)n clusters (n = 1–5), as measured by mass-selective, ionization-loss stimulated Raman spectroscopy. The spectra exhibit prominent Raman activity in the range 35–65 cm−1. In addition, Raman bands at less than 10 cm−1 are found for the n = 1 and n = 3 species, and rotational Raman features are observed for all of the clusters. It is argued that much of the Raman activity is due to intermolecular vibrations in which water moieties move collectively across the plane of the benzene.