FORBIDDEN TRANSITIONS INVOLVING HIGHLY EXCITED TORSIONAL STATES IN METHANOL-D-1 AND CONFIRMATION OF OPTICALLY PUMPED FAR-INFRARED LASER LINES

'Forbidden' transitions involving highly excited torsional levels in t he ground vibrational state of methanol-D-1 (CH2DOH) have been identif ied in the high resolution Fourier transform spectrum, which become al lowed through 'Fermi' interaction with the first excited OCD-bend stat e. This is the first time such transitions have been identified for an y asymmetric-asymmetric molecule and rep resents a breakthrough in the assignments for torsional-rotational transitions of singly deuterated asymmetric methanol. This provides data for the modeling of the torsi on-mediated interaction Hamiltonian. The results also confirm the assi gnment of far-infrared (FIR) emissions involving an upshifted pump tra nsition to the OCD-bend state, the mechanism of the anomalous shift of which remained a mystery until now. In addition, comments have been m ade for the anomalous intensity of the OCD-bend transitions for differ ent symmetry species. (C) 1998 Elsevier Science B.V. All rights reserv ed.