Determination of line intensity and pressure broadening of the 619.68 nm methane overtone absorption line at low temperatures using intracavity laser spectroscopy

Abstract The temperature dependence of the line intensity and of the pressure broadened width of the 619.68 nm absorption line in the Δν CH = 6 overtone rotational-vibrational band of methane is studied experimentally. Measurements are performed in the temperature range between 77 and 296 K and with H 2 , N 2 and He as foreign-gas collisional partners. Absorption spectra of methane at low temperatures and with a variety of pressure conditions are recorded by intracavity laser spectroscopy (ILS) to obtain large (0.7–60 km) equivalent absorption pathlengths. The line intensities and pressure broadening coefficients determined here demonstrate that quantitative spectroscopic data can be derived from a lineshape analysis of ILS data. The significance of these results with respect to observational spectroscopy of planetary atmospheres is discussed.