Methyl chloride (CH3Cl) plays an important role in the catalytic destruction of ozone in the lower stratosphere. One of the methods used to determine the concentration of this gas in the atmosphere is the study of the 3.4 µm region by infrared spectroscopy, and specifically of the QQ sub branches of the ν1 band. For this, spectroscopic parameters of very high quality are needed. So we studied at the laboratory, the spectroscopy of CH3Cl in this spectral region. High resolution spectra were recorded using a Fourier transform spectrometer. Positions and intensities were measured from spectra of pure CH3Cl at low pressure. These measurements enabled fitting an effective Hamiltonian including six interacting states and the dipole moment matrix. It was then possible to calculate line positions and intensities of 22 963 transitions in the region near 3.4 µm. Then, to complete the modeling of this spectral region, the lineshape was studied. The self- and N2-broadening coefficients were measured for atmospheric temperatures (200-300 K). A model describing the rotational dependence of these coefficients and their temperature dependence was performed. Finally, the linemixing effect between transitions inside QQ branches was observed and modeled. The measurements and calculations allowed to build a complete line list in the region of 3.4 µm, improving significantly the existing ones in the databases
