Energy distributions of neutrons scattered from solid C₆₀ by the beryllium detector method

Abstract

We measured the energy distribution of neutrons scattered from polycrystalline C 60 , using a high-resolution filter-analyzer spectrometer. In the energy range 30–90 meV (242–726 cm −1 ) we observed a rich spectrum that we fitted to a sum of 15 Gaussian functions, each of which is assigned to one or a set of several degenerate normal vibrational modes of the C 60 molecule. We also observed two broad features in the energy range from 90–130 meV (726–1049 cm −1 ). Our results are generally in excellent agreement with published spectroscopic data. Detailed comparisons with the results of several first-principles calculations suggest that present-day theories can predict the internal vibrational frequencies of C 60 rather well, at least in the 30–90 meV range of energies.