Fourier transform synchrotron spectroscopy of the COD-bending fundamental of CD3OD

Abstract

The high-resolution Fourier transform spectrum of the CD3OD isotopologue of methanol in the region of the COD-bending fundamental band at 775 cm−1 has been recorded at the Far Infrared Beamline of the Canadian Light Source synchrotron. The torsion-rotation structure has been analyzed for sub-bands from K = 0 to 16 for both A and E torsional symmetries in the vt = 0 torsional state of the COD-bending mode. Energy term values for the excited COD-bending levels have been determined, and fitted to J(J + 1) power-series expansions to provide substate J = 0 origins. These have in turn been fitted to a basic Fourier model in order to map the torsional energy structure. The K-reduced COD-bending torsional origins follow a regular oscillatory pattern as a function of K with a significantly reduced amplitude relative to that of the vibrational ground state. With use of a simple formula for the change in the torsional constant F, the torsional barrier height V3 is found to be 440.25 cm−1, an increase of 22% relative to the ground state. The COD bend does not show evidence of anharmonic Fermi resonances with the ground torsional manifold, but J-localized level-crossing resonances coupling the 5A and 8A substates with vt = 4 ground level partners have been observed and characterized.