Ab initio determination of the far infrared spectra of some isotopic varieties of ethanol

The far infrared (FIR) spectra of various isotopic species of ethanol (-h(6 ), -d(1), and -d(3)) are analyzed from MP4((SDQT) ab initio calculations us ing models in one and two dimensions. From the calculated frequencies and i ntensities, previous assignments of ethanol-h(6) and -d(1) bands are review ed. The position of several combination bands are predicted. Ethanol shows two conformers, trans and gauche, and two interacting torsional modes. The torsional barriers have been calculated to be V-3((trans)) = 1226.7 cm(-1), V-3((gauche)) = 1296.3 cm(-1), V-OH(alpha = 62 degrees) = 404.1 cm(-1), an d V-OH(alpha = 180 degrees) = 423.3 cm(-1). The flexible models in one and two dimensions yields the same OH torsional frequencies, whereas they diffe r in the methyl group state calculations. The fundamental bands of the etha nol-h(6) have been evaluated at 205.5 cm(-1) (OH torsion) and 257.0 cm(-1) (CH3 torsion) and their corresponding intensities to be 18.650 x 10(-4) and 0.662 x 10(-4). (C) 2000 American Institute of Physics. [S0021-9606(00)516 13-4].