Temperature dependences of N2-broadening and shift coefficients in the ν6 perpendicular band of 12CH3D

- FT-IR study of the line parameters for the ν6 band of CH3D broadened by N2.
- Measurement and modeling of temperature dependences of CH3D-N2 ν6 line parameters
- Simultaneous fittings of 23 high-resolution FTS spectra from 296 to 75 K
- Line mixing retrieved using the off-diagonal relaxation matrix formalism
- 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 cm−1 unapodized resolution) using the McMath−Pierce 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 cm−1 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 (0≤J″≤19, K″≤16) in the perpendicular (ΔK=±1) ν6 band. At 296 K, the measured N2-broadened half-width coefficients range from 0.0209 to 0.0782 cm−1 atm−1 whereas the majority of the associated N2-induced shift coefficients are negative, and the values are between -0.016 and 0.005 cm−1 atm−1. 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 cm−1 atm−1 K−1. 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 J″ 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.