TEMPERATURE-DEPENDENCE OF RAMAN-SCATTERING IN VAPOR-GROWN C-60 CRYSTALS

The temperature dependence of the Raman spectra of vapour-grown C-60 c rystals is investigated with deep-red excitation. The excitation using a deep-red laser can avoid a photo-induced transformation of C-60 cry stals during the Raman measurement. It is found that discontinuous cha nges occur in the Raman spectra at the SC-FCC phase transition tempera ture (260 K). Most intramolecular vibrational modes broaden drasticall y as the temperature exceeds 260 K. Crystal-field splitting of the int ramolecular vibrational modes is observed below 260 K. The broadening of the Raman bands would be caused by the increase in the inhomogeneit y of intermolecular force fields in the FCC phase. This broadening cor responds to the increase in the orientational disorder of C-60 molecul es above the phase transition.