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 collec tive vibrational modes in the ground states of benzene dimer, trimer, tetramer, and pentamer by mass-selective, ionization-loss stimulated R aman spectroscopy at 0.2 cm-1 resolution. The spectra are markedly siz e-dependent and become complex rapidly with increasing size. The polar ization characteristics of the spectra and the deuterium-isotope effec ts on them suggest that almost all of the observed bands correspond to intermolecular vibrations that have some librational character. The r esults are discussed in terms of the properties of the clusters and ar e compared to spectra of intermolecular vibrations in condensed-phase samples of benzene.