Raman study of a structural phase transition in C60 crystals.

Raman spectra of purified C 60 single crystals are measured over a wide temperature range. It is found that above 400 K the high-frequency A g mode (pentagonal pinch mode) changes in frequency and becomes sharp compared with the A g mode at room temperature. This spectral change is reversible. The results indicate that structural change occurs and the intermolecular interaction for each C 60 molecule is isotropic above 400 K