ANALYSIS OF THE LOWEST IN-PLANE BEND AND FIRST EXCITED TORSIONAL STATE OF CH$_3$CH$_2$CN

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 Title: ANALYSIS OF THE LOWEST IN-PLANE BEND AND FIRST EXCITED TORSIONAL STATE OF CH$_3$CH$_2$CN Creators: Brauer, Carolyn S.; Pearson, John C.; Drouin, Brian J.; Yu, Shanshan Issue Date: 2009 Publisher: Ohio State University Abstract: Propionitrile (CH$_3$CH$_2$CN) is observed with large column densities in a number of high-mass star-forming cores, where core temperatures exceed 200 K. It is a near-prolate ($\kappa=0.96$) asymmetric top with appreciable dipole moment components on both the $a-$ and $b-$axes ($\mu_a = 3.84$ D, $\mu_b = 1.23$ D).,\textbf{29a},1345 (1974).} This, combined with the presence of four fundamental modes as well as four overtones and combination bands all occurring below 600 cm$^{-1}$, results in a very rich spectrum. It is known to be a major contributor to spectral line confusion in ground-based observations and is expected to complicate observations by Herschel, SOFIA and ALMA, making it imperative to fully characterize the entire spectrum. The lowest in-plane bend, $\nu_{13}$, is 206.9(0.5) cm$^{-1}$,,\textbf{90},531 (1981).} and the first excited torsional state, $\nu_{21}$, which is just 186 GHz above, have been detected in hot cores with antenna temperatures of a few Kelvin.,\textbf{608},306 (2004).} The close proximity of $\nu_{13}$ and $\nu_{21}$, as well as their low-lying nature, offers a unique opportunity to study the vibration-torsion-rotation coupling problem in the case of two nearly degenerate vibrational states. As expected from $C_s$ symmetry and their $A^\prime$ and $A^{\prime\prime}$ nature, these states exhibit strong $a-$ and $b-$symmetry Coriolis interactions, as well as interactions resulting from different sets of Eckhart-Sayvetz conditions being required in $\nu_{13}$ and $\nu_{21}$. In the present work, the $\nu_{13}$ and $\nu_{21}$ states of propionitrile have been analyzed to high frequency and angular momentum quantum number. The spectrum, molecular constants,and insights into the vibration-torsion-rotation problem will be discussed. Description: H.~M.~Heise, H.~Lutz \& H.~Dreizler,\textit{Z.Nat.H.~M.~Heise, F.~Winther \& H.~Lutz,\textit{J. Mol. Spectrosc.D.~M.~Mehringer, J.~C.~Pearson, J.~Keene \& T.~G.~Phillips,\textit{Ap.J.Research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration. Author Institution: JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY, 4800 OAK GROVE DR., PASADENA, CA 91109 URI: http://hdl.handle.net/1811/38336 Other Identifiers: 2009-TC-07