Temperature dependences of air-broadening, air-narrowing and line-mixing coefficients of the methane nu 3 R(6) manifold lines-Application to in-situ measurements of atmospheric methane

In this work, we have revisited the spectroscopy of the R(6) manifold of the nu 3 band of methane which is particularly suitable for in situ laser monitoring of CH4. For that purpose, a home-made Difference Frequency Generation (DFG) laser emitting at 3.24 mu m has been coupled to a cryogenically-cooled optical cell to investigate the temperature dependences of the air-broadening, the air-narrowing and the air-mixing coefficients of these nu 3 R(6) manifold transitions. The temperatures of the measurements range from 213.5 K to room temperature. These are typically the temperatures found in the troposphere and the lower stratosphere. Finally, the measured spectroscopic parameters have been used to process the in-situ methane absorption spectra recorded by a balloon-borne laser diode spectrometer.