LATTICE PHONON MODES IN SOLID C-60 STUDIED BY FAR-INFRARED SPECTROSCOPY

The far-infrared transmission spectrum of solid C60 is presented in the 7.5-420-cm-1 range at 2 K. It is found that the cubic environment of C60 molecules in the solid results in the activation and splitting of silent molecular modes. The two infrared-active translational modes propagating in the C60 solid are observed below 60 cm-1. Their energies are found to be significantly higher than predicted by molecular-dynamics simulations. This suggests a harder intermolecular potential for solid C60 than presently used in these simulations.