N2-broadening coefficients of methyl chloride at room temperature

Methyl chloride is of interest for atmospheric applications, since this molecule is directly involved in the catalytic destruction of ozone in the lower stratosphere. In a previous work [Bray et al. JQSRT 2011;112:2446], lines positions and intensities of self-perturbed CH3Cl and CH3Cl have been studied into details for the 3.4 μm spectral region. The present work is focused on measurement and calculation of N2-broadening coefficients of the CH3Cl and CH3Cl isotopologues. High-resolution Fourier Transform spectra of CH3Cl-N2 mixtures at room-temperature have been recorded between 2800 and 3200 cm at LADIR (using a classical source) and between 47 and 59 cm at SOLEIL (using the synchrotron source on the AILES beamline). 612 mid-infrared transitions of the ν1 band and 86 far-infrared transitions of the pure rotational band have been analyzed using a multispectrum fitting procedure. Average accuracy on the deduced N2-broadening coefficients has been estimated to 5% and 10% in the midand far-infrared spectral regions, respectively. The Jand K-rotational dependences of these coefficients have been observed in the mid-infrared region and then a simulation has been performed using an empirical model for 0 ≤ J ≤ 50, K ≤ 9. The CH3Cl-N2 line widths for 0 ≤ J ≤ 50 and K ≤ 10 of the ν1 band and for 55 ≤ J ≤ 67 and K ≤ 15 of the pure rotational band have been computed using a semiclassical approach involving exact trajectories and a real symmetric-top geometry of the active molecule. Finally, a global comparison with the experimental and theoretical data existing in the literature has been performed. Similar Jand K-rotational dependences appeared while no clear evidence for any vibrational and isotopic dependences have pointed out. ha l-0 07 46 01 0, v er si on 1 29 O ct 2 01 2