MOLECULAR-DYNAMICS OF C-60 IN SUPERCONDUCTING NA2CSC60

We have measured the low-energy inelastic neutron scattering spectra o f superconducting Na2CsC60 in the temperature range 100-350 K. Well-de fined librational peaks are observed at 2.7(1) meV; their position and width are temperature independent. They survive well above the order- disorder transition at 299 K. A quasielastic feature with a width 1.03 (6) meV at an average scattering vector of 1.09 Angstrom(-1) is observ ed at 350 K, arising from diffusive motion of the C-60(3-) ions. Evide nce is found for influence of the Na+ ions on the rotational motion of the C-60(3-) ions.