Fourier transform spectroscopy of the OD-bending band of CH3OD

Abstract

The infrared Fourier transform spectrum of the OD-bending fundamental band of the CH3OD isotopologue of methanol has been investigated and analyzed in the 745–945 cm−1 region. The OD-bend is of hybrid a–b type, with predominantly parallel a-type character plus a small admixture of perpendicular b-type structure. The K-structure in the central Q-branch region is unusually well resolved and shows substantial shading to higher wavenumber. Sub-bands have been assigned for the vt = 0 ground torsional state from K = 0 to 13 for both A and E torsional species, as well as a number of sub-bands in the vt = 1, 2 excited torsional states. Upper-state term values have been determined from the observations and fitted to J(J + 1) power-series expansions to explore the torsion–K-rotation energy structure of the excited OD-bending state. A simple Fourier model for the energy structure gives a wavenumber of 863.246 cm−1 for the vt = 0 origin of the OD-bending band. The K = 0 torsional (E − A) splitting of 2.456 cm−1 found for the vt = 0 OD bend is 5.6% smaller than that of the ground state, and would correspond to a 9.9 cm−1 increase in the torsional barrier height, V3, to a value of approximately 376.2 cm−1 if other parameters do not change.