Self- and air-broadened line shape parameters in the ν2+ν3 band of 12CH4: 4500–4630 cm−1. (February 2015)

• Record Type: Journal Article
• Authors: Devi, V. Malathy; Benner, D. Chris; Smith, Mary Ann H.; Mantz, Arlan W.; Sung, Keeyoon; Crawford, Timothy J.; Predoi-Cross, Adriana
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 152(2015:Feb.)
• Page Start: 149
• Page End: 165
• Publication Date: 2015-02
• Subjects: Methane -- Lorentz width -- Pressure-shift -- Temperature dependence -- Speed dependence -- Relaxation matrix; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2014.11.011
• Languages: English
• ISSNs: 0022-4073

Abstract

Abstract: Accurate knowledge of spectral line shape parameters is important for infrared transmission and radiance calculations in the terrestrial atmosphere. In this paper, we report the self- and air-broadened Lorentz half-widths, pressure-induced shifts and line mixing coefficients (via off-diagonal relaxation matrix elements) along with their temperature dependences for methane ν2 +ν3 absorption lines in the 4500–4630 cm −1 region of the Octad. For this, we recorded 14 high-resolution, high signal to noise ratio (S/N) spectra of high-purity (99.95% 12 C-enriched) samples of pure methane and its dilute mixtures in dry air between 298 K and 148 K. A Bruker IFS 125HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California, was used to obtain the experimental data. The absorption cell used for this study was a specially built 20.38 cm long coolable cell installed in its sample compartment. The sample pressures for the pure 12 CH4 spectra were 4.5−385 Torr; for the air-broadened spectra the total pressures ranged between 95 and 300 Torr with the methane volume mixing ratios between 0.04 and 0.097. All 14 spectra were fitted simultaneously using an interactive multispectrum nonlinear least-squares curve fitting technique. The results are compared to values reported in the literature. Highlights: First measurements of low temperature self-broadening parameters in 12 CH4 ν2 +ν3 . 14 High resolution room- and low-temperature spectra were fitted simultaneously. Temperature dependences of self- and air-broadened half-widths were measured. Temperature dependences of self- and air-pressure-shift coefficients were measured. Comparisons of widths, shifts, and line mixing with previous studies are presented.