First high resolution measurement of the centrifugal distortion spectrum of methane (CH4) - AILES beamline
Methane is a small molecule present in many planetary atmospheres, including that of the Earth (where it is a powerful green-house gas), Mars, giant planets, Titan (Saturn’s satellite), giant exoplanets and brown dwarfs. Due to its great symmetry, the methane molecule does not possess a permanent dipole moment. Centrifugal distortion can, however, induce a very weak pure rotational spectrum. This is very important in planetology as it allows, in particular, the quantity of methane in Titan’s atmosphere to be measured using the CIRS instrument in the (NASA/ESA) Cassini probe. Until now, measurements have been based on old, low-resolution laboratory data.
We measured for the first time this high resolution spectrum (0.0011 cm-1) on the infra-red AILES beamline, with an optical path length of 150 m. The data obtained will permit the absolute intensities in this region to be measured. The resulting model will act as a reference for interpreting data on present and future space missions.
