Vibrational Modes

Publisher Summary This chapter reviews the lattice mode structure for the isolated fullerene molecules and for the corresponding molecular solid. The major experimental techniques for studying the vibrational spectra include Raman and infrared spectroscopy, inelastic neutron scattering, and electron energy loss spectroscopy. Of these techniques, the most precise values for vibrational frequencies are obtained from Raman and infrared spectroscopies. In most crystalline solids, Raman and infrared spectroscopy measurements focus primarily on first-order spectra which are confined to zone-center (q = 0) phonons. Because of the molecular nature of fullerene solids, higher-order Raman and infrared spectra also give sharp spectral features. Analysis of the second-order Raman and infrared spectra for C60 provides a good determination of the 32 silent mode frequencies and their symmetries. If large single crystals are available, then the most general technique for studying solid-state phonon dispersion relations is inelastic neutron scattering. Unfortunately, large single crystals are not yet available even for C60, so that almost all the reported inelastic neutron scattering measurements have been done on polycrystalline samples. Much of the emphasis of the inelastic neutron scattering studies thus far has been on the lowest-energy intermolecular dispersion relations, which have been studied on both single-crystal and polycrystalline samples.