Using FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈ 0.001 cm −1) of methyl bromide CH 3 Br, absolute line positions and intensities, as well as self-and N 2broadening coefficients have been measured for about 1200 lines, between 880 and 1050 cm −1 , in the 6 ν band of both 12 CH 3 79 Br and 12 CH 3 81 Br isotopologues. An absolute wavenumber calibration has been performed using the frequencies of the 2 ν band of NH 3. 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. Average absolute accuracies of the measurements have been estimated to be equal to ± 0.0002 cm −1 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 6 ν band. The J and K dependences of the self-and N 2-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 N 2-broadening coefficients for which clear J-and K-dependences have been observed and modeled. A complete line list containing line positions, intensities, self-and N 2-broadening coefficients has then been generated for atmospheric purposes from 820 to 1120 cm −1 .

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Following our recent study devoted to measurements of intensities of rovibrational lines in the ν 6 band of methyl iodide (12 CH 3 I) centered at 892.918 cm −1 , room temperature infrared spectra of methyl iodide diluted in nitrogen at fourteen total pressures between 20 and 300 hPa have been recorded using the Fourier transform spectrometer Bruker IF125HR located at the LISA facility in Créteil. Three hundred and forty six N 2-broadening coefficients of methyl iodide rovibrational lines have been measured in the 824-951 cm −1 spectral range using mono-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects could be neglected. Six hundred and eight self-broadening coefficients have also been measured in the same spectral range using the pure methyl iodide spectra recorded in our previous work. The measured self-broadening coefficients range from 0.1460 to 0.3786 cm − 1 atm −1 and the N 2-broadening coefficients range from 0.0723 to 0.1481 cm −1 atm − 1 at 295 K. The average accuracy on the measured self-and N 2-broadening coefficients was estimated to 3%. Comparisons with measurements reported in the literature for the ν 5 band of CH 3 I shows a satisfactory agreement with average differences of 7% and 4% for the self-and N 2-broadening coefficients, respectively. The J and K rotational dependences of these coefficients have been observed and the latter modeled using an empirical polynomial expansion. On average, the empirical expression reproduces the measured self-and N 2-broadening coefficients to within 3% and 4%, respectively. The data obtained in the present work represent a significant contribution to the determination of broadening coefficients of CH 3 I and complement the list of line positions and intensities generated in our previous work, thus providing useful spectroscopic information for atmospheric remote sensing and industrial detection of CH 3 I.

Context. Dimethyl sulfide, CH 3 SCH 3 (DMS), is a nonrigid, sulfur-containing molecule whose astronomical detection is considered to be possible in the interstellar medium. Very accurate spectroscopic constants were obtained by a laboratory analysis of rotational microwave and millimeter wave spectra, as well as rotation-torsional far-infrared (FIR) spectra, which can be used to predict transition frequencies for a detection in interstellar sources. Aims. This work aims at the experimental study and theoretical analysis of the ground torsional state and ground torsional band ν 15 of DMS in a large spectral range for astrophysical use. Methods. The microwave spectrum was measured in the frequency range 2−40 GHz using two Molecular Beam Fourier Transform MicroWave (MB-FTMW) spectrometers in Aachen, Germany. The millimeter spectrum was recorded in the 50−110 GHz range. The FIR spectrum was measured for the first time at high resolution using the FT spectrometer and the newly built cryogenic cell at the French synchrotron SOLEIL. Results. DMS has two equivalent methyl internal rotors with a barrier height of about 730 cm −1 . We performed a fit, using the XIAM and BELGI-C s -2Tops codes, that contained the new measurements and previous transitions reported in the literature for the ground torsional state ν t = 0 (including the four torsional species AA, AE, EA and EE) and for the ground torsional band ν 15 = 1 ← 0 (including only the AA species). In the microwave region, we analyzed 584 transitions with J ≤ 30 of the ground torsional state ν t = 0 and 18 transitions with J ≤ 5 of the first excited torsional state ν t = 1. In the FIR range, 578 transitions belonging to the torsional band ν 15 = 1 ← 0 with J ≤ 27 were assigned. Totally, 1180 transitions were included in a global fit with 21 accurately determined parameters. These parameters can be used to produce a reliable line-list for an astrophysical detection of DMS.

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