Optically detected librons and phonons in crystallineC60

Abstract
Well-defined intermolecular modes of crystalline C60 were studied by means of Fourier-transform Raman and far-infrared spectroscopy. The librational modes are seen to gradually soften and broaden in energy as the temperature is raised from 10 to ∼260 K at which point the libron intensity abruptly vanishes, consistent with the order-disorder phase transition. The librational modes, which are in general agreement with the less well-resolved neutron-scattering results, are found to be remarkably sharp at low temperature.