Article révisé par les pairs
Résumé : The far infrared spectrum of methane is observed in emission in the stratosphere of Titan, Saturn's main satellite, allowing to determine its concentration in this environment. However this spectrum, which has a very low intensity because it is induced by the centrifugal distortion of the molecule only, was poorly characterized up to now. For the first time, it has been recorded, in absorption and at high resolution, at the AILES beamline of the SOLEIL synchrotron. Measurements have been performed for both pure methane and methanenitrogen mixtures. The intensities of methane lines and coefficients characterizing the broadening of these lines induced by collisions with nitrogen have been accurately determined. These new spectroscopic data, essential to analyze measurements in planetology, will most probably improve our understanding of physicochemical processes in planetary atmospheres where methane is often present.

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