Infrared spectroscopy through the orientational phase transition in fullerene films

Infrared-absorption studies of thin fullerene films as a function of temperature reveal a splitting of an absorption line at 245±3 K. Another absorption line narrows and its frequency shifts without splitting. These observations support earlier neutron- and x-ray-diffraction findings of an orientational phase transformation at 250 K in bulk samples. We provide an explanation based on an accepted crystal structure of ${\mathrm{C}}_{60}$.