TORSION-ROTATION FAR-INFRARED SPECTRUM OF O-18 METHANOL

High-resolution Fourier transform spectra have been recorded from 15-4 70 cm-1 for the far-infrared torsion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15-220 cm-1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an es timated accuracy of +/-0.01 cm-1. The observed origins were found to d eviate in many cases by several tenths of a cm-1 from the values calcu lated with the previous molecular parameters. Together with 4 known mi crowave origins, the new data have been fitted to a model torsion-rota tion Hamiltonian in order to refine the set of b-type molecular consta nts for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of +/-0.02 cm-1, rep resenting a substantial improvement over the earlier situation. The sp ectroscopic results have also been of great assistance with our assign ments of optically-pumped FIR laser emission in CH3(18)OH, in providin g FIR data for checking the identification of the IR-pump/FIR-laser tr ansition systems through combination loop relations.