GLOBAL FIT ANALYSIS INCLUDING THE $\nu_{9}+\nu_{4}-\nu_{4}$ HOT BAND OF ETHANE: EVIDENCE OF INTERACTION WITH THE $\nu_{12}$ FUNDAMENTAL
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Date
2006
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Ohio State University
Abstract
The $\nu _{9}$ (methyl rock) fundamental band of ethane occurs in the 12 $\mu $m region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The $\nu _{9}+\nu _{4}-\nu _{4}$ band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here a global fit model including data from the $\nu_{3}$ (C-C stretch) fundamental, the $\nu_{4}$, $2\nu_{4}-\nu_{4}$, and $3\nu_{4}$ torsional transitions, the $\nu_{9}$ fundamental, and its $\nu_{9}+\nu_{4}-\nu_{4}$ hot band. The combined data set of more than 4000 lines has been fitted to within experimental uncertainty using a model Hamiltonian which includes many terms which were important in analyzing the corresponding hot band of CD$_{3}$CD$_{3}$. We have therefore identified Coriolis interactions with the ground vibrational state (gs) for both the $\nu_{9}$ and $\nu_{9}+\nu_{4}-\nu_{4}$ bands, as well as gs/$\nu_{3}$ Fermi coupling, and have determined several barrier-dependence terms which were not previously accessible. More remarkably, we have also identified a new, resonant interaction with the $\nu_{12}$ fundamental which -- unlike terms included in previous models -- is off-diagonal in the torsional quantum number $\sigma$.
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Author Institution: Department of Physics and Astronomy, 2500 University Drive NW, Calgary,; Alberta T2N 1N4, Canada