The ν1, ν4 and 3ν6 bands of methyl chloride in the 3.4 µm region: line positions and intensities

Methyl chloride (CH3Cl) is one of the most abundant chlorine-containing molecules in the atmosphere. For this reason a recent update was performed by Iouli Gordon (private communication) in HITRAN in the 640-2600 cm-1 region using line parameters generated by A. Nikitin, et al. [Nikitin A Champion JP, and Bürger H. J Mol Spectrosc 2005;230:174-184]. CH3Cl has a rather strong signature around 3000 cm-1 which was used recently by the Atmospheric Chemistry Experiment (ACE) satellite mission to produce the first study of the global distribution of methyl chloride in the upper troposphere and stratosphere. However it was mentioned that the CH3Cl line positions and intensities spectroscopic parameters are of very low quality in this spectral region in the public access HITRAN or GEISA databases. We present a complete update of the line positions and line intensities for the ν1, ν4, 3ν6 bands of CH335Cl and CH337Cl in the 3.4 µm region. For this task, Fourier transform spectra have been recorded at high resolution in "Laboratoire de Dynamique, Interactions et Réactivité" (LADIR). Measurements of line positions and line intensities have been retrieved for both isotopologues 12CH335Cl and 12CH337Cl in the ν1, ν4, 3ν6 bands. The theoretical model accounts for the interactions coupling the (v1=1; =0), (v4=1; =±1) and (v6=3; =±1) energy levels, together with additional resonances involving several dark states.