Infrared and Raman Spectra, Vibrational Assignments, Normal Coordinate Analysis, and ab Initio Calculations of Methyltrifluoromethyldisulfide and Bis(trifluoromethyl)disulfide

The infrared and Raman (3500-35 cm(-1)) spectra of gaseous and solid methyltrifluoromethyldisulfide, CF3SSCH3, and bis(trifluoromethyt)disulfide, CF3SSCF3, have been recorded. Additionally, the Raman spectra of the neat liquids have been obtained and qualitative depolarization values have been measured. These vibrational data have been interpreted, for both molecules, on the basis that the C-S-S-C dihedral angle is approximately 90 degrees Vibrational assignments are given for both molecules and are supported by normal coordinate calculations utilizing ab initio Hartree-Fock gradient calculations with the 3-21 G* basis set to obtain the frequencies for the normal modes and potential energy distributions. The CH3 and CF3 torsional modes have been observed at 140 and 48 cm(-1), respectively, for CF3SSCH3, from which periodic barriers of 485 cm(-1) (1.39 kcal mol(-1)) and 853 cm(-1) (2.44 kcal mol(-1)), respectively, have been calculated. Complete equilibrium geometries have been determined for both molecules by ab initio calculations employing both 3-21G* and 6-31 G* basis sets. The structural parameters for bis(trifluoromethyl) disulfide are compared to those suggested from electron diffraction studies. The results are compared to corresponding quantities obtained for some similar molecules.