Orientational states of C_(60) molecule in crystals

摘要

Local symmetry of orientational states of the C_(60) molecule in crystals has been investigated. It was shown that the various orientational phase transitions in different crystals are related to different orientational 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 tighter after a reduction of crystal spatial symmetry at the phase transition. This effect is fairly common and can be observed in the orientational order-disorder phase transitions with wave vectors at the Brillouin zone boundary. Feasible manifestations of the predicted effect in various experiments are discussed.