Fine band structure of the vibrational spectra of fullerite C60 and enhancement of intermolecular interaction in high-temperature phase

Abstract

The fine structure of the fundamental vibrational bands and some combination tones of fullerite C60 in its IR absorption and reflection spectra, as well as in Raman spectra, has been studied. This structure is due to the overlapping components of Davydov and isotopic splittings and the removal of vibrational degeneracy with symmetry lowering. It is shown that for IR Fu(i) bands (i = 1–4) and low-frequency Hg(1) and Ag(1) bands in the Raman spectrum the splittings at room temperature exceed those for the low-temperature phase. The enhancement of intermolecular interaction at elevated temperatures is explained by the nonequilibrium vibrational excitation of the medium as a result of nonlinear interaction of vibrational modes and by the change in the electronic states.