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Title: Giant K-doubling and in-plane/out-of-plane mixing in the asymmetric methyl-bending bands of CH 3SH

In analyzing high-resolution spectra of the methyl-deformation bands of methyl mercaptan recorded at the Canadian Light Source synchrotron, we have encountered interesting interactions between certain levels of the ν 4 in-plane asymmetric CH 3-bending mode and its ν 10 out-of-plane bending partner below. The origin of the K = 0A ν 4 substate is just 0.2 cm -1 higher than that of the K = 2A ν 10 substate, while the K = 0E ν 4 origin is only 0.035 cm -1 below the K = 2E ν 10 origin. These very close accidental near-degeneracies lead to substantial perturbations in the spectrum. For the former, the A +/A - asymmetry K-doublet coupling rules are such that the A - component of the 2A ν 10 doublet interacts and mixes strongly with the 0A + ν 4 levels whereas the 2A + component is unaffected. The 2A - levels are pushed rapidly downwards by the coupling creating an extremely large apparent K = 2A asymmetry splitting. We call this “giant K-doubling” by analogy with a comparable phenomenon seen for methanol. The 0A + ν 4 state, in turn, is perturbed upward and passes through the descending K = 1A + νmore » 4 state between J = 22 and 23, leading to distinct local perturbations near the level-crossing. The 0E ν 4 and 2E ν 10 coupling produces a correspondingly strong repulsion and mixing between those two substates, and gives rise to a forbidden K = 0 ← 3E intermode sub-band in the spectrum via intensity borrowing.« less
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  1. Univ. of New Brunswick, Saint John, NB (Canada). Centre for Laser, Atomic and Molecular Sciences (CLAMS). Dept. of Physics
  2. Lamar Univ., Beaumont, TX (United States). Dept. of Chemistry and Biochemistry
  3. Univ. of Akron, OH (United States). Dept. of Chemistry
  4. Univ. of Saskatchewan, Saskatoon, SK (Canada). Canadian Light Source Inc.
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Journal of Molecular Spectroscopy
Additional Journal Information:
Journal Volume: 335; Journal ID: ISSN 0022-2852
Research Org:
Univ. of Akron, OH (United States); Univ. of New Brunswick, Saint John, NB (Canada); Univ. of Saskatchewan, Saskatoon, SK (Canada)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Natural Sciences and Engineering Research Council of Canada (NSERC)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; methyl mercaptan; CH3SH; internal rotation; CH3-bending bands; infrared spectra; torsion-vibration interactions
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1425385