Neutron scattering study of a high-pressure polymeric C₆₀ phase

The vibrational spectrum of a high-pressure phase of C₆₀ prepared at 21 kbar and 620 K was studied by inelastic neutron scattering and compared with the spectrum of the simple cubic phase restored in the same sample by vacuum annealing at 620 K. The intermolecular band of the restored cubic phase is between 2 and 7 meV and resembles that of pristine C₆₀. The spectrum of the high-pressure phase shows a strong band with 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 intermolecular vibrations in pristine C₆₀. 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 the range of the tangential intramolecular modes, 110-220 meV. The experimental data for the high-pressure phase are in reasonable agreement with the infinite-chain polymerization model.