ANALYSIS OF THE LOWEST LYING DEGENERATE FUNDAMENTAL OF $CH_{3}CD_{3}$

The lowest lying vibrational fundamental $(v_{12}-l-O)$ in $CH_{3}CD_{3}$ has been studied between 640 and $720 cm^{-1}$ using a modified Bomem spectrometer with an unapodized resolution of $0.0013 cm^{-1}$. The experimental conditions were: $path=2 m, T=-145 C, P=0.4 Torr$; and $path=2 m, T-22 C, P=1.2 Torr$. Over 1000 transitions have been identified obeying the selection rules $\Delta v_{6}=1 \Delta(k-1)=0$, and $\Delta J=0,\pm$ with $\Delta v_{6}=\Delta \sigma 0$, where $v_{6}$ is the principal torsional quantum number and $\sigma$ labels the torsional sublevels. The data clearly reveal that many of the $(v_{12}=1, v_{6}=0)$ levels are resonantly perturbed by $(v_{12}=0, v_{6}-3)$ levels of the ground vibrational state for several different $(k,\sigma)$. The perturbation can be accounted for using a Hamiltonian $model1$ explicitly including the effect of the Coriolis interaction and a higher order Coriolis-like term that arises from the off-diagonal part of the operator responsible for the l-type doubling. The overall data set consists of 4 microwave transitions and molecular beam data$^{2}$ in the ground vibrational state, in addition to the lines from the $\nu_{12}$ band up to $K=11$ and $J=15$. The model fits the observed frequencies to within experimental error except for transitions connected to the levels $(v_{12}=1, K=2, \sigma 1, 1=1)$ for $J>6$. These levels are severely perturbed and undergo a crossover.

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$^{1}$ N. Moazzen-Ahmadi, I. Ozier, and W.L. Meerts, J. Mol. Spectrosc., to be published. $^{2}$ I. Ozier and W.L. Meerts, Can. J. Phys. 62, 1844-1854 (1984).
Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics, University of British Columbia

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http://hdl.handle.net/1811/17804

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Abstracts of OSU International Symposium on Molecular Spectroscopy 1980-1989

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