Theoretical investigation of the torsional spectra of 2,2,2-trifluoroethanol

The structure and the torsional spectra of various isotopic varieties of 2,2,2-trifluoroethanol (TFE) are investigated with MP4(SDQ)/cc-pVTZ ab initio calculations. The energy levels corresponding to the CF3 and the OH internal rotation modes, are calculated variationally. With the predicted frequencies and intensities, previous assignments are reviewed. The position of several combination bands are predicted. The most stable conformation of TFE has a gauche geometry which is stabilized by the formation of intramolecular F-H hydrogen bonds. A second trans conformer lies 681.5 cm(-1) over the gauche form. The torsional barriers have been calculated to be V-3((gauche)) = 1534.0 cm(-1), V-3((trans)) - 1490.9 cm(-1), V-OH(alpha = 34 degrees) = 707.5 cm(-1) and V-OH(alpha = 180 degrees) = 804.9 cm(-1). The fundamental bands of the gauche-TFE have been evaluated at 286.7 and 283.3 cm(-1) (OH torsion) and 115.0 and 114.9 cm(-1) (CF3 torsion) and their corresponding intensities to be 21.73 x 10(-4) and 23.16 x 10(-4), and 0.009 x 10(-4) and 0.002 x 10(-4), respectively. (C) 2001 Elsevier Science B,V. Ah rights reserved.