Fourier transform synchrotron spectroscopy of torsional and CO-stretching bands of CH 317OH

Abstract

The Fourier transform spectrum of the CH 3 17OH isotopologue of methanol has been recorded in the 65–1200 cm −1 spectral region at a resolution of 0.00096 cm −1 using synchrotron source radiation at the Canadian Light Source. Here we present an extension to higher torsional states of our investigation of the torsion–rotation transitions within the small-amplitude vibrational ground state, now including assignments of more than 16 500 lines involving quantum numbers in the ranges v t ⩽ 3, J ⩽ 30 and | K| ⩽ 12, as well as a study of the strong CO-stretching band centered at 1020 cm −1. Energy term values have been determined for assigned ground and CO-stretching levels by use of the Ritz program, and have been fitted to series expansions in powers of J( J + 1) to determine substate origins and effective B values. Several Fermi anharmonic and Coriolis level-crossing resonances coupling the CO stretch with high torsional ground-state levels have been identified and characterized. The study is motivated by astrophysical applications, with a principal aim being the compilation of an extensive set of energy term values to permit prediction of astronomically observable sub-millimetre transitions to within an uncertainty of a few MHz.