NEUTRON-SCATTERING STUDY OF A HIGH-PRESSURE POLYMERIC C-60 PHASE

The vibrational spectrum of a high-pressure phase of C-60 prepared at 21 kbar and 620 K was studied by inelastic neutron scattering and comp ared with the spectrum of the simple cubic phase restored in the same sample by vacuum annealing at 620 K. The intermolecular band of the re stored cubic phase is between 2 and 7 meV and resembles that of pristi ne C-60. The spectrum of the high-pressure phase shows a strong band w ith maxima at 12.8 and 16.6 meV and a minor peak around 5.2 meV, and, thus, demonstrates new interball modes at higher energies than the int ermolecular vibrations in pristine C-60. Only minor energy shifts and splitting of some vibrational bands were observed in the high-pressure phase in the energy range of 25-110 meV, corresponding to the radial intramolecular modes, but the measured spectra markedly differed in th e range of the tangential intramolecular modes, 110-220 meV. The exper imental data for the high-pressure phase are in reasonable agreement w ith the infinite-chain polymerization model.