Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5427925 | Journal of Quantitative Spectroscopy and Radiative Transfer | 2015 | 22 Pages |
â¢FT-IR study of the line parameters for the ν6 band of CH3D broadened by N2.â¢Measurement and modeling of temperature dependences of CH3D-N2 ν6 line parametersâ¢Simultaneous fittings of 23 high-resolution FTS spectra from 296 to 75 Kâ¢Line mixing retrieved using the off-diagonal relaxation matrix formalismâ¢Catalogued all measured line parameters for use in remote sensing applications.
The temperature-dependences of line broadening and shift parameters for many 12CH3D transitions have been determined using six high-resolution, high signal-to-noise ratio, room-temperature CH3D (98% purity) and CH3D-N2 spectra recorded with 25 cm path length ( at 0.01 cmâ1 unapodized resolution) using the McMathâPierce FTS located on Kitt Peak, Arizona, and 17 additional high quality, pure CH3D (99% purity) and CH3D-N2 spectra recorded between 79 and 296 K with the 20.38 cm path coolable cell (at 0.0056 cmâ1 unapodized resolution) with the Bruker 125HR FTS at the Jet Propulsion Laboratory (JPL), Pasadena, California. The spectra have been fitted simultaneously applying a multispectrum nonlinear least-squares technique. In the analysis, the Lorentzian N2-broadened half-width coefficients and the corresponding pressure-shift coefficients as well as their temperature dependences are extracted for about 400 transitions (0â¤Jâ³â¤19, Kâ³â¤16) in the perpendicular (ÎK=±1) ν6 band. At 296 K, the measured N2-broadened half-width coefficients range from 0.0209 to 0.0782 cmâ1 atmâ1 whereas the majority of the associated N2-induced shift coefficients are negative, and the values are between -0.016 and 0.005 cmâ1 atmâ1. The temperature dependence exponents for N2-broadened half-widths range between 0.264 and 0.924, whereas the temperature dependence coefficients for N2-induced shifts are between 0 and 0.00011 cmâ1 atmâ1 Kâ1. The N2-broadened half-width coefficients have been also calculated using a semi-classical approach 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. The role of the various high-order multipoles in the line-broadening at low, middle and high values of the rotational quantum number Jâ³ has been investigated and the main features of the K-dependences analyzed. The calculations performed for 296, 240 and 190 K have allowed to deduce the half-width temperature-dependence exponents, completing the general comparison of our new experimental results with those which are available in the literature.