FAR-INFRARED SPECTRUM OF METHYLAMINE AND THE GROUP THEORETICAL TREATMENT OF ITS LARGE AMPLITUDE MOTIONS
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Date
1986
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Ohio State University
Abstract
We report here the results of a study of the far-infrared spectrum of methylamine obtained on the NBS BOMEM DA3.002 Fourier transform spectrometer. The spectrum was recorded in the wavenumber region 50 to $350 cm^{-1}$ with an apodized resolution of 0.004 and $0.005 cm^{-1}$. The torsional band, as well as pure rotational transitions with higher $K_{a}$, fall in this wavenumber region. This molecule has two large amplitude motions, the $NH_{2}$-wag and the $CH_{3}$-torsion. The spectrum is complicated because of splittings arising from these motions. Assignments were made using polynomial fittings of individual subbands. The $B_{1}(B_{2})-B_{2}(B_{1})$ and $E_{1}-E_{1}$ transitions were assigned for each subband. Preliminary analysis, carried out using approximate energy level formulae, gives a value for the torsional tunneling parameter in the $v=1$ excited torsional state which is about 30 times larger than the value for the ground state, in good agreement with the earlier work of M\""{o}ller and $coworkers^{1}$. We have also carried out a group theoretical treatment for the problem of the large amplitude motions, and have obtained energy level formulae which are expected to be applicable for the global fit of the assigned transitions in the spectrum. This formalism was constructed by applying the concepts of extended permutation-inversion groups.
Description
$^{1}$C. Belorgeot, V. Stern, N. Goff, J. Kachmarsky and K. D. M\""{o}ller. J. Mol. Spectrosc. 92, 91-100 (1982). Address of Ohashi: Department of Physics, Faculty of Science, Kanazawa University, Kanazawa 920, Japan. Address of Takagi: Department of Physics, Faculty of Science, Toyama University, Toyama 930, Japan. Address of Lafferty, Olson and Hougen: Molecular Spectroscopy Division, National Bureau of Standards, Gaithersburg, MD 20899.
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