Vibrational spectra of the α-crystalline phase of hexafluoroethane

A synthesis of spectral evidence and x-ray data has resulted in the solution of the crystal structure of the a form of hexafluoroethane. The space group is Cy, with two molecules in the unit cell located on C, sites. The unit-cell dimensions are a =9.3 A, 6 =5.1 A, and c =4.6 A. There is disorder in the a crystal which was determined to be of the statistical variety. The spectra of the a form verified the symmetry aspects of the theory governing solid-state vibrational spectroscopy, but the approximate dipole-dipole theory was shown to partially fail in explaining even the relative magnitudes of the splittings in the nondegenerate modes. This failure was ascribed to atom-atom interactions in the crystal.