A COMBINED FREQUENCY ANALYSIS OF THE $\nu_{3}, \nu_{9}$, AND THE FAR INFRARED TORSIONAL SPECTRA OF ETHANE
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Date
2000
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Ohio State University
Abstract
The lowest frequency nondegenerate fundamental band $\nu_{3}$ of ethane is Raman active and centered near $992 cm^{-1}$. A stimulated Raman spectrum of the Q branch for this band (at a resolution of $0.0055 cm^{-1}$) has been recorded by Bermejo $et al.^{a}$ The torsion-rotation branch with $\sigma = 3$ is perturbed by over $1 cm^{-1}$. The lowest frequency degenerate fundamental band $\nu_{9}$ is infrared active and occurs in the $12-\mu m$ region. A high resolution $(0.0014 cm^{-1})$ Fourier transform spectrum of this band has been measured by Moazzen-Ahmadi $et al.^{b}$. The observed torsional splittings for this band are substantially larger than expected simply from the observed increase in the barrier height. Because of the proximity of the upper level $(l=-1; K=17, \sigma=0)$ in $\nu_{9}=1$ with its interacting partner $(\nu_{9}=0, \nu_{4}=3)$ a perturbation allowed band $3\nu_{4}$ has also been observed. We have carried out a combined frequency analysis of $\nu_{3}, \nu_{9}$, and $3\nu_{4}$ bands together with the far infrared torsional spectra in the ground vibrational state (gs). A vibration-torsion-rotation Hamiltonian with 32 fitting parameters was used. Three interacting torsional stacks, one for each of the vibrational state, were considered. The large torsional splitting in the $\nu_{9}$ band is attributed to Coriolis-like interations between the torsional stacks of gs and $\nu_{9} = 1$ whereas the large shift for the torsion-rotation branch with $\sigma = 3$ in the $\nu_{3}$ band is attributed to a Fermi-like interaction between the torsional stacks of gs and $\nu_{3} = 1$. The details of this analysis will be presented.
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$^{a}$ D. Bermejo, J. Santos, P. Cancio, J. M. Fernandez-Sanchez, and S. Montero, J. Chem. Phys. 97, 7055 (1992). $^{b}$ N. Moazzen-Ahmadi, J. Schroderus, and A.R.W. McKellar, J. Chem. Phys. 111, 9609 (1999).
Author Institution: Department of Physics and Astronomy, University of Calgary
Author Institution: Department of Physics and Astronomy, University of Calgary