			15min:

THE ROTATION-TORSION SPECTRUM OF CH₂DOH.

A. EL HILALI, L. H. COUDERT, LISA, CNRS/Universités Paris Est et Paris Diderot, 61 Avenue du Général de Gaulle, 94010 Créteil, France; L. MARGULÈS, R. MOTIYENKO, Laboratoire PhLAM, UMR 8523 CNRS, Bât. P5, Université des Sciences et Technologies de Lille 1, 59655 Villeneuve d'Ascq Cedex, France; AND S. KLEE, Physikalisch-Chemisches Institut, Justus-Liebig-Universität Gieß en, 35392 Gieß en, Germany.

Due to the asymmetry of the CH₂D group, the internal rotation problem in the partially deuterated species of methanol CH₂DOH is a complicated one as, unlike in the normal species CH₃OH, the inertia tensor depends on the angle of internal rotation. The CH₂DOH species also displays a dense far infrared torsional spectrum difficult to assign. Recently 38 torsional subbands of CH₂DOH have been identified, but for most of them there is neither an assignment nor an analysis of their rotational structure.

In this paper an analysis of the rotation-torsion spectrum of CH₂DOH will be presented. The rotational structure of 23 torsional subbands have been assigned. These subbands are Delta v_t \geq 1 perpendicular subbands with a value of v'_t up to 10^b and values of K' and K'' ranging from 0 to 9. For all subbands, the Q-branch was assigned, for 3 subbands, the R- and P-branches could also be found. The results of the rotational analysis with an expansion in J(J+1) of the new subbands and of already observed ones\footnote[3]Quade, Liu, Mukhopadhyay, and Su, J.~Mol.~Spec. ~ 192 (1998) 378; and Mukhopadhyay, J.~Mol.~Struct. ~ 695-696 (2004) 357. will be presented. When available, microwave lines within the lower torsional level, recorded in this work or already measured,\footnote[4]Liu and Quade, J.~Mol.~Spec. ~ 146 (1991) 252; and Mukhopadhyay et al., J.~Chem.~Phys. ~ 116 (2002) 3710. were added to the data set.

A theoretical approach aimed at calculating the rotation-torsion energy levels has also been developed. It is based on an expansion in terms of rotation-torsion operators with C_s symmetry and accounts for the dependence of the inertia tensor on the angle of internal rotation. This approach will be used to carry out a preliminary global analyses of the wavenumbers and of the frequencies.