Inversion of the Ka = 0 and 1 rotational levels in the lowest excited vibrational state of HNCS |
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Authors: | K Yamada M Winnewisser G Winnewisser LB Szalanski MCL Gerry |
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Institution: | Physikalisch-Chemisches Institut, Justus Liebig-Universität, D-6300 Giessen, West Germany;Max-Planck-Institut für Radioastronomie, D-5300 Bonn, West Germany;Department of Chemistry, The University of British Columbia, Vancouver, B. C. Canada, V6T 1W5 |
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Abstract: | Fairly strong, regularly spaced absorption lines have been observed in the microwave spectrum of HNCS and assigned to b-type, Ka = 0 ← 1, Q-branch transitions arising from molecules in the lowest excited vibrational state. The Fortrat diagram of these lines has the appearance of a c-type Q branch, which is impossible in HNCS because of its symmetry. This anomalous b-type Q-branch spectrum is caused by strong a-type Coriolis interactions among the three low-lying bending modes; the Ka = 1 levels of the lowest excited vibrational state are perturbed and shifted lower in energy than the Ka = 0 levels for each J. This interpretation has been confirmed by the observation of P- and R-branch transitions associated with this Q branch. The band origin has been determined to be ?40 104.287 MHz (?1.3377 cm?1). The inversion of the Ka = 0 and 1 energy levels is consistent with the interpretation of HNCS as a quasi-linear molecule. |
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