M. SMIRNOV, L. H. COUDERT, LISA, CNRS/Universités Paris 12 et 7, 61 Avenue du Général de Gaulle, 94010 Créteil, France; S. BLASCO, D. LAUVERGNAT, Laboratoire de Chimie Physique, Unité mixte du C.N.R.S. et de l'Université Paris-Sud, Bât. 490, Université Paris-Sud, 91405 Orsay Cedex, France; AND S. KLEE, Physikalisch-Chemisches Institut, Justus-Liebig-Universität Gieß en, 35392 Gieß en, Germany.

Although the torsional spectrum of the isotopic species of methanol with a symmetrical CH3 or CD3 methyl group has been studied in great details, almost no investigations have been carried out on partially deuterated species of methanol, like CH2DOH or CD2HOH, with an asymmetrical CH2D or CD2H methyl group. This stems from the fact that these partially deuterated species of methanol require a complicated theoretical treatment in order to compute their rotation-torsion energy levels and that they display a dense far infrared torsional spectrum difficult to assign.

With a view toward understanding this spectrum, a theoretical calculation of the rotation-torsion energy levels of CH2DOH has been undertaken aided by ab initio calculations. This approach accounts for the complicated torsion-rotation interaction displayed by this molecule and for the fact that, due to the low symmetry of the CH2D methyl group, the inertia tensor is strongly dependent on the torsional angle of rotation. In the theoretical approach, this angle is treated as an active coordinate and matrix elements of the kinetic energy part of the Hamiltonian, involving the inertia tensor, are calculated using Gaussian quadrature.\footnoteLight and Bacić, J. Chem. Phys. ~ 87, 408 (1987). Rotation-torsion energy levels are obtained using a potential energy function retrieved through ab initio calculations.

In the paper, a calculated rotation-torsion spectrum will be presented and compared to the experimental one, recorded in Gieß en. It will be shown that this allows us to assign about 50 torsional bands.