A complete set of line parameters for CH3Br in the 10-microns spectral region
Résumé
Using FT spectra (Bruker IFS 120, unapodized FWHM resolution ̴ 0.001 cmˉ¹) of methyl bromide CH3Br, absolute line positions and intensities, as well as self- and N2-broadening coefficients have been measured for about 1200 lines, between 880 and 1050 cmˉ¹, in the band of both 12CH379Br and 12CH381Br isotopologues. An absolute wavenumber calibration has been performed using the frequencies of the band of NH3. A multispectrum fitting procedure has been used to retrieve simultaneously the line parameters from 6 experimental spectra recorded at different pressures of CH3Br and N2. Average absolute accuracies of the measurements have been estimated to be equal to +/- 0.0002 cmˉ¹ for line positions, to +/- 5% for line intensities, and to +/- 5-10% for broadening coefficients. A theoretical treatment of measured line positions permitted a prediction of positions and assignments for the whole 10-µm spectral region. Measured line intensities have been analyzed in order to predict the intensities for the whole band. The J and K dependences of the self- and N2-broadening coefficients have been observed and modeled. These measurements improve the precision of wavenumbers and line intensities previously obtained and lead us, for the first time, to a complete set of self- and N2-broadening coefficients for which clear J- and K-dependences have been observed and modeled. A complete line list containing line positions, intensities, self- and N2-broadening coefficients has then been generated for atmospheric purposes from 820 to 1120 cmˉ¹.
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