A Complete Set of Line Parameters for CH3Br inthe 10-πm Spectral Region

Methyl bromine is of interest for atmospheric applications, since this molecule is directly involved in the catalytic destruction of ozone in the lower stratosphere. At the present time no spectroscopic data is available in the atmospheric databases as HITRAN or GEISA. Using FT spectra (Bruker IFS 120, unapodized FWHM resolution of 0.001 cm ^-1 ) of methyl bromide CH 3 Br, absolute line positions and intensities, as well as self-and N 2 - broadening coe±cients have been measured for about 1200 lines between 880 and 1050 cm ^-1 in the v6 band of ^12CH3 ^79Br and 12^CH3 81^Br. These measurements improve the accuracy on wavenumbers and line intensities previously obtained and lead to a complete set of self- and N 2 -broadening coe±cients for which clear J -and K -dependences have been observed for the first time. A multispectrum fitting procedure has been used to retrieve simultaneously the line parameters from 6 experimental spectra recorded at different pressures of CH 3 Br and N 2 . A wavenumber calibration has been performed using the line frequencies of the v2 band of NH 3 . Average absolute accuracies of the measurements have been estimated around 0.0005 cm ^-1 for line positions, 5% for line intensities, and 5-10% for broadening coe±cients. A theoretical treatment of wavenumbers permitted the prediction of assignments and wavenumbers for the whole 10- π m spectral region. Line intensities have been analyzed to deduce the eÆective vibrational transition moment squared as well as Herman-Wallis coe±cients. Self-and N 2 -broadening coe±cients have been reduced using an empirical polynomial expansion function of J and K . A complete line list containing line positions, intensities, self- and N 2 -broadening coe±cients has then been generated for atmospheric purposes with all lines from 820 to 1120 cm ^-1 having intensities greater than 10 ^-5 cm ^-2 ¢ atm ^-1 .