Observation of lattice phonon modes in solid C60 at 2 K

A dense compact pellet of C60 is examined experimentally in the 7-240/cm region of the far-IR transmission spectrum, and the results are compared to those of molecular-dynamics calculations. The chromatographic method set forth by Allemand et al. (1991) is employed to study the 4-mm powder pellet, and the optical spectra are recorded by means of the Fourier transform technique with a resolution of 2/cm. Two primary regions of transmission spectra are observed: one with frequencies of more than 340/cm and one with frequencies less than 75/cm. The two regions are highly structured and correspond to the phonon modes of solid C60 or to the normal modes of the C60 molecule. The results are in agreement with molecular dynamics calculations that give the librational modes at less than 19/cm.