N _2-broadening coefficients of methyl chloride at room temperature

摘要

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 ~(12)CH _3 ~(35)Cl and ~(12)CH _3 ~(37)Cl have been studied into details for the 3.4μm spectral region. The present work is focused on measurement and calculation of N _2-broadening coefficients of the ~(12)CH _3 ~(35)Cl and ~(12)CH _3 ~(37)Cl isotopologues. High-resolution Fourier Transform spectra of CH 3Cl-N _2 mixtures at room-temperature have been recorded between 2800 and 3200cm ~(-1) at LADIR (using a classical source) and between 47 and 59cm ~(-1) at SOLEIL (using the synchrotron source on the AILES beamline). 612 mid-infrared transitions of the ν _1 band and 86 far-infrared transitions of the pure rotational band have been analyzed using a multispectrum fitting procedure. Average accuracy on the deduced N _2-broadening coefficients has been estimated to 5 and 10 in the mid- and far-infrared spectral regions, respectively. The J- and 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 ~(12)CH _3 ~(35)Cl-N _2 line widths for 0≤J≤50 and K≤10 of the ν _1 band and for 55≤J≤67 and K≤15 of the pure rotational band have been computed using a semi-classical 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 J- and K-rotational dependences have been appeared while no clear evidence for any vibrational or isotopic dependences have been pointed out.