THE SIZE DEPENDENCE OF GROUND-STATE COLLECTIVE VIBRATIONAL-MODES IN MOLECULAR CLUSTERS - BENZENE DIMER THROUGH PENTAMER

We report the measurement of species-selective Raman spectra of collective vibrational modes in the ground states of benzene dimer, trimer, tetramer, and pentamer by mass-selective, ionization-loss stimulated Raman spectroscopy at 0.2 cm-1 resolution. The spectra are markedly size-dependent and become complex rapidly with increasing size. The polarization characteristics of the spectra and the deuterium-isotope effects on them suggest that almost all of the observed bands correspond to intermolecular vibrations that have some librational character. The results are discussed in terms of the properties of the clusters and are compared to spectra of intermolecular vibrations in condensed-phase samples of benzene.