THE FAR-INFRARED SPECTRUM OF CRYSTALLINE C60

The infrared spectrum of crystalline C60 has been measured in the frequency range 500-20 cm-1 at various temperatures between 300 and 10 K. Since no dipole-allowed intramolecular vibration is active below 500 cm-1, the infrared absorption is determined by crystal and quadrupolar interactions. Davydov splittings of several intramolecular vibrations have been observed. The infrared activity of H(g) modes is discussed. In the lattice region the two translational phonons of T(u) symmetry are observed at 41 and 58.5 cm-1 at 8 K. Considerations on the order-disorder phase transition Of C60 Crystal are advanced on the basis of our experimental results.