ORIENTATIONAL STATES OF C-60 MOLECULE IN CRYSTALS

Local symmetry of orientational states of the C-60 molecule in crystal s has been investigated. It was shown that the various orientational p hase transitions in different crystals are related to different orient ational orbits. The model of orientational phase transitions based on a sequence of orientational states with different symmetry properties has been suggested. We have found that both the local symmetry of C-60 molecule and the symmetry of its internal vibrations become higher af ter a reduction of crystal spatial symmetry at the phase transition. T his effect is fairly common and can be observed in the orientational o rder-disorder phase transitions with wave vectors at the Brillouin zon e boundary. Feasible manifestations of the predicted effect in various experiments are discussed. (C) 1998 American Institute of Physics. [S 1063-7761(98)02503-7].