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Author(s):Kobayashi, Kaori
Contributor(s):Billinghurst, Brant E.; Tokaryk, Dennis W.; Ohashi, Nobukimi ; Fujitake, Masaharu ; ITOH, AKIO
Subject(s):Mini-symposium: Large Amplitude Motions
Abstract:The known interstellar molecule, methyl formate (HCOOCH$_3$) has been studied by microwave spectroscopy since 1959 \footnote{R. F. Curl, \textit{J. Chem. Phys.} \underline{\textbf{30}}, 1529 (1959).}. The laboratory spectra of methyl formate exhibit many unassigned transitions and are due to rotational transitions in the low-lying vibrational excited states. The first torsional excited state was reported in 2003 $\footnote{H. Odashima, K. Ogata, K. Takagi, \& S. Tsunekawa, \textit{Molecules} \underline{\textbf{8}}, 139 (2003).}$, and up to the second torsional excited state was identified in laboratory and in space. $\footnote{S. Takano, Y. Sakai, S. Kakimoto, M. Sasaki, \& K. Kobayashi, \textit{Publ. Astron. Soc. Jpn.} \underline{\textbf{64}}, 89 (20012).}$ $\footnote{K. Kobayashi, K. Takamura, Y. Sakai, S. Tsunekawa, H. Odashima, \& N. Ohashi, \textit{Astrophys. J. Suppl. Ser.} \underline{\textbf{205}}, 9 (2013) and references therein.}$ Our laboratory microwave spectra include a series of unknown $K_a$=0,1 transitions. Based on relative intensities, we estimate that these transitions arise from an excited state about 300 cm$^{-1}$ above the ground state. To facilitate identification, we have taken spectra of methyl formate in the 260-370 cm$^{-1}$ range at Far-Infrared Beamline of the Canadian Light Source synchrotron. The resolution was instrument-limited to 0.00096 cm$^{-1}$. The spectra were very dense, and included the overlapping $\nu_{12}$ (C-O-C deformation) and $\nu_{17}$ (C-O torsion) modes. Conventional assignment proved very difficult, so we calculated a-type $K_a$ =0, and 1 rotation-vibration spectra based on the unknown and ground-state microwave data, and gave them arbitrary origins near 300 cm$^{-1}$. By correlating them with the far-infrared spectrum, we were able to determine that the new series correspond to $\nu_{12}$ near 312 cm$^{-1}$.$\footnote{K. Kobayashi, Y. Sakai, M. Fujitake, D. W. Tokaryk, B. E. Billinghurst \& N. Ohashi, \textit{Submitted to Can. J. Phys.}}$ We will report on our assignment technique and results, as well as any further developments we have made in extending the assignments of both the microwave and far-infrared spectra.
Issue Date:23-Jun-20
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Date Available in IDEALS:2020-06-26

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