TORSIONAL SPECTRA OF $CH_{3}CH_{3}$ AND $CD_{3}CD_{3}$: INTENSITY ANALYSIS
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Date
1991
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Publisher
Ohio State University
Abstract
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.
Description
Author Institution: Department of Physics, University of Lethbridge; Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics, University of British Columbia