A note on CH3OD spectra, ground-state energies and FIR laser assignments

Literature data on the CO-stretching and the ground-state torsion rotation spectra of the CH3OD isotopic species of methanol have been exploited to ex trapolate the ground-state energies to higher J through use of ground-state combination differences derived from the CO-stretching wavenumbers. In par ticular, the J-dependence has been extended and better defined for the diff icult \K \ = 0 to 2 E energy level sequences, which are strongly affected b y molecular asymmetry. The pattern of the J-dependence is found to be quali tatively well reproduced by a simple 11 x 11 Hamiltonian model incorporatin g DeltaK = +/-1 and +/-2 off-diagonal asymmetry matrix elements. The result s suggest partial reassignment of certain CO-stretching subbands, and the K = 8 and 9 A subbands have been newly identified through clues from reporte d far-infrared laser (FIRL) emission. Transition combination loops support a number of FIRL line assignments previously proposed, but show that the FI RL system pumped by the 9R(4) CO2 line must be reassigned.