TORSIONAL SPECTRA OF $CH_{3}CH_{3}$ AND $CD_{3}CD_{3}$: INTENSITY ANALYSIS

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1991

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Ohio State University

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Spectra of gaseous $CH_{3}CH_{3}$ and $CD_{3}CD_{3}$ have been recorded using a modified Bomem spectrometer. For $CD_{3}CD_{3}$, the region of the torsional fundamental (208 $cm^{-1}$) was measured at a resolution of $0.016 cm^{-1}$ and an absorption path length of 20 m. The gas temperature and pressure were 168 K and 80 Torr, respectively. In addition, the $\nu_{9}$ fundamental (650 $cm^{-1}$) was studied at very high resolution ($0.0014 cm^{-1}$) with a path length of 2 m at a temperature of 133 K and a pressure of 0.6 Torr. The ground state torsion-rotation parameters were obtained from a combination of (I) a frequency analysis of 442 lower state combination differences in $\nu_{9}$ band and its associated hot band $\nu_{9} + \nu_{4} - \nu_{4}$ with (II) a frequency/intensity analysis of the P, Q, and R branches of the torsional fundamental and the Q branch of the first torsional overtone. The torsional dipole moments $\mu_{1}$ and $\mu_{|}-\mu_{\perp}$ were determined to be 7.41(74) and -19.9(2.0) $\mu $D, respectively. Similar measurements and analyses were carried out for $CH_{3}CH_{3}$. The torsional dipole moments are: $\mu_{\perp} = 9.27(93)$ and $\mu_{|}-\mu_{\perp} = -30.81(3)$ $\mu $D. The experimental values of $\mu_{\perp}$ and $\mu_{|}-\mu_{\perp}$ are shown to be in excellent agreement with values calculated from theoretical expressions. The shape of the torsional bands can be reproduced in detail with the model used.

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Author Institution: Department of Physics, University of Lethbridge; Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics, University of British Columbia

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