Multispectrum analysis of air-broadened spectra in the ν3 Q branch of 12CH4. (February 2018)

• Record Type: Journal Article
• Authors: Devi, V. Malathy; Benner, D. Chris; Gamache, Robert R.; Tran, H.; Smith, Mary Ann H.; Sams, Robert L.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 206(2018)
• Page Start: 409
• Page End: 429
• Publication Date: 2018-02
• Subjects: Methane -- 12CH4 -- ν3 Q branch -- Relaxation matrix element coefficients -- Lorentz air broadening -- Air pressure-induced shifts -- Speed dependence; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2017.12.005
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: Line shape parameters for v 3 Q branch transitions of 12 CH4 near 3015 cm −1, Room temperature measurements of air-broadened widths and shifts. Off-diagonal relaxation matrix element coefficients for CH4 -air collisions. Air-broadened widths and shifts compared with HITRAN2012 values. Positions for 252 and intensities for 274 transitions are obtainede. Abstract: We report experimental measurements of spectral line shape parameters (air-broadened width, shift, and line mixing coefficients) for several transitions in the ν3 Q branch of methane in the 3000–3023 cm −1 region. 13 high-resolution, room temperature laboratory spectra of pure methane and air-broadened methane recorded with two different Fourier transform spectrometers are fitted. 12 of these spectra were acquired at 0.01 cm −1 resolution with the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak, and one higher-resolution (∼0.0011 cm −1 ) low pressure methane spectrum was obtained with the Bruker IFS-120HR FTS at the Pacific Northwest National Laboratory, in Richland, Washington. All the spectra were obtained using high purity natural samples of CH4 and lean mixtures of the same natural CH4 in dry air. For the 12 spectra recorded at Kitt Peak, three different absorption cells (L = 5, 25 and 150 cm) were used while the methane spectrum at PNNL was obtained using a 19.95 cm long absorption cell. For the analysis, an interactive multispectrum nonlinear least squares fitting software was employed where all the 13 spectra were fitted simultaneously. An accurate and self-consistent set of line parameters were determined by constraining a few of those for severely blended transitions. Line mixing was measured for 14 transition pairs for the CH4 -air collision system. A constant speed dependence parameter, consistent with measured speed dependence values obtained in other methane bands, was applied to all the transitions included in the fitted region. The present measurements are compared to values reported in the literature.