Vibrational spectra of the α-crystalline phase of hexafluoroethane

Abstract

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 C2h2 with two molecules in the unit cell located on Ci sites. The unit-cell dimensions are a = 9.3 Å, b = 5.1 Å, and c = 4.6 Å. 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.

Fermi resonances in the vibrational spectrum of perfluoroethane

“…On the whole, the results of [5][6][7] are in satisfactory agreement with one another and until recently did not cause doubts. observed in [5][6][7].…”

“…observed in [5][6][7]. However, the presence of Fermi resonances of states m 1 $ 2m 6 (A 1g ) and m 7 $ 2m 8 $ m 6 + m 11 (E g ) was recently predicted in paper [8].…”

“…At present, the Raman spectrum of this molecule is not studied thoroughly. All modern researchers interested in the frequencies of Raman bands of the perfluoroethane molecule (C 2 F 6 ) in the regions of fundamental transitions (for example, in order to estimate the results of ab initio calculation, for example [3,4]) refer to papers [5][6][7]. This data were obtained in the 1950-1970s.…”

“…The Raman spectrum of liquid C 2 F 6 is studied in [5,7]. It is necessary to note that the main purpose of [7] was to study the vibrational spectrum of an a-crystalline phase of perfluoroethane.…”

“…The Raman spectrum of liquid C 2 F 6 is studied in [5,7]. It is necessary to note that the main purpose of [7] was to study the vibrational spectrum of an a-crystalline phase of perfluoroethane. In addition, the authors of [7] also reported the band frequencies of liquid C 2 F 6 but they did not present any spectra of the liquid and data on band intensities.…”