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R. M. LEES, LI-HONG XU AND ANNA K. KRISTOFFERSON, Department of Physical Sciences, University of New Brunswick, Saint John, NB, Canada E2L 4L5; MICHAEL LOCK AND B. P. WINNEWISSER, Physikalisch-Chemisches Institut, Justus Liebig University, D-35392 Giessen, Germany; J. W. C. JOHNS, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON, Canada K1A 0R6.
The high-resolution Fourier transform spectrum of CH3OH has been investigated in the 1400-1650 cm-1 region, containing the CH3-bending fundamental bands. Twenty-two perpendicular
K = +1 subbands have been identified so far, with origins ranging from 1490 to 1570 cm-1 for transitions K = 2
1 up to 11
10 for various torsional symmetries. Assignment of the subbands to the
4 in-plane (A') or
10 out-of-plane (A'') asymmetric methyl-bending modes is not yet clear, but the one subband so far observed with resolved K-doublet structure suggests c-type selection rules consistent with a
10 vibrational assignment. The pattern of the K-reduced torsion-vibration energy
-curves is inverted compared to the normal 1-dimensional picture for n = 0 torsional levels, in agreement with prediction based on fitting torsional variation of ab initio CH3-bending frequencies to a local mode model. However, the periodicity of the curves is unusual and significantly different from the ground state. The vibrational energy for the bending mode is 1481 cm-1, and the mean B-value is 0.008 cm-1 higher than that of the vibrational ground state.