Measured And Theoretical Self- And N₂-Broadened Line Parameters In The Ν₆ Band Of Ch₃D
Creators: name: Devi, V. Malathy
name: Benner, D. Chris
name: Sung, Keeyon
name: Predoi-Cross, Adriana
name: Smith, Mary Ann H.
name: Mantz, Arlan W.
name: Sinyakova, Tatyana
name: Buldyreva, Jeanna
Publisher: name: Zenodo
Year: 2014
Subjects: Poster Session
Spectroscopy
Methane
Temperature variation

description: Monodeuterated methane (CH<sub>3</sub>D) is a constituent trace species in several planetary atmospheres, and its spectrum is often used in determinations of atmospheric <em>H/D </em>ratios. Methane plays an important role in terrestrial atmospheric chemistry. It is the most abundant hydrocarbon in our atmosphere and as an <em>IR </em>active gas makes an important contribution to the enhanced greenhouse effect. Methane is increasing in the Earth’s atmosphere at a rate of about 1% per year. The current knowledge of its sources and sinks are not sufficient to isolate the cause of the observed changes in the mixing ratio and global distribution. As a result, the infrared spectrum of methane and its isotopomers is continually being investigated in order to obtain improved spectroscopic line parameters needed to interpret remote sensing observations. Remote sensing instruments require laboratory data sets based on measurements of very high accuracy.

The primary objective of this study is to enhance our spectroscopic knowledge of monodeuterated methane in the <em>ν</em><sub>6 </sub>band located at 6.8 microns. We present measurement results for self- and N<sub>2</sub>-broadened line parameters from room temperature down to about 80 <em>K</em>. A total of 23 high-resolution, high <em>S/N </em>spectra recorded with two Fourier transform spectrometers: a) the McMath-Pierce FTS located on Kitt Peak and b) a Bruker IFS-125HR FTS at the Jet Propulsion Laboratory (JPL) <sup>1</sup> were fit simultaneously in a multispectrum approach.<sup> 2 </sup>The set included both pure CH<sub>3</sub>D and dilute mixtures of CH<sub>3</sub>D in research grade nitrogen. The variations in the measured line parameters with the symmetry species, the rotational quantum numbers and with temperature are reported and discussed in comparison with earlier measurements.

For the case of nitrogen-broadening, we also provide semi-classical calculations based on a rigorous treatment of the active molecule as a symmetric top, a model intermolecular potential comprising both short- and long-range interactions, and exact classical trajectories. These calculations are done for various temperatures and for wide ranges of rotational quantum numbers. The role of the various high-order multipoles in the line-broadening at low, middle and high values of the rotational quantum number <em>J </em>is investigated. Main features of the <em>K</em>-dependences are also analyzed. These theoretical values are included in the general comparison of our new experimental and already available in the literature results. <sup>3</sup>
description: Poster Session II: June 24, 2014.
description: {"references": ["K. Sung et al., J. Mol. Spec. 262 122-134 (2010).", "D. Chris Benner et al., JQSRT 53 705-721 (1995).", "Research described in this work was performed at the College of William and Mary, Jet Propulsion Laboratory, California Institute of Technology, Connecticut College and NASA Langley Research Center under contracts and cooperative agreements with the National Aeronautics and Space Administration. A. Predoi-Cross was funded by NSERC, Canada."]}