N-2-broadening coefficients of methyl chloride: Measurements at room temperature and calculations at atmospheric temperatures

作者：Ramchani A Barbouchi; Jacquemart D^*; Dhib M; Aroui H

来源：Journal of Quantitative Spectroscopy and Radiative Transfer, 2014, 148: 186-196.

DOI：10.1016/j.jqsrt.2014.07.008

• Methyl chloride
• Fourier transform spectroscopy
• N-2-broadening coefficients
• J- and K-dependences
• Semi-classical calculation
• Temperature dependence exponent

Infrared spectroscopic study on methyl chloride is the first step for its accurate detection in the atmosphere. In our previous work [Barbouchi Ramchani et al. J Quant Spectrosc Radiat Transfer 2013;120:1-15], line positions, intensities and self-broadening coefficients of both (CH3Cl)-C-12-Cl-35 and (CH3Cl)-C-12-Cl-32 isotopologues have been studied in the 6.9 mu m spectral region. The present work is focused on measurements of N-2-broadening coefficients for transitions of (CH3Cl)-C-12-Cl-35 and (CH3Cl)-C-12-Cl-37 around 6.9 mu m. For that, high-resolution Fourier transform spectra of CH3Cl-N-2 mixtures have been recorded at room temperature using a rapid scan Bruker IFS 120 HR interferometer at LADIR. The N-2-broadening coefficients have been retrieved using a Voigt profile and a multispectrum fitting procedure. The average accuracy of the N2-broadening obtained in this work has been estimated to be between 5% and 10% depending on the transitions. The rotational J- and K-dependences of the N-2-broadening coefficients have been clearly observed and modeled using empirical polynomial expansions. The (CH3Cl)-C-12-Cl-35-N-2 line-widths of the nu(5) band have also been computed using a semi-classical approach for the R-P, R-R and R-Q sub-branches. A global comparison with the experimental data from this work but also existing in the literature was then performed. Similar J- and K-rotational dependences have been observed while no clear evidence of any vibrational or isotopic dependence has been pointed out. Finally, performing theoretical calculations of the N-2-broadening coefficients at various temperatures of atmospheric interest between 200 and 296 K allowed deducing the temperature exponent of the (CH3Cl)-C-12-Cl-35-N-2 line-widths.

• 出版日期2014-11