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V. Vuitton, M. C. Gazeau, J. F. Doussin, P. Carlier, F. Raulin (L.I.S.A., UMR 7583)
A new program coupling experimental simulations and theoretical modelling has been developed in the context of the Cassini-Huygens mission, in order to study specific reactions occurring in Titan's atmosphere. Mixtures of gases are irradiated at 185 nm with low pressure Hg lamps in an 1 m3 atmospheric simulation chamber. The products are analysed in situ with a very long path FT-IR spectrometer and it is also possible to take aliquots from the reacting mixture for further analysis using GC-MS. The first study performed is in concern with the catalytic dissociation of methane by acetylene. This process has been suggested to explain the concentrations of hydrocarbons in Titan's stratosphere. We will present and discuss results concerning irradiation of a CH4/C2H2 mixture (100/1)) and will provide quantitative data on the formation of C2H4, C2H6, C3H4, C3H6, C3H8 and C4H2. A O-D theoretical study adapted to our experimental conditions has been carried out in parallel. A critical comparison between experimental and theoretical results will be presented. Extrapolation of these results to an open system will enable us to perform a critical comparison with existing gas-phase schemes in order to improve the chemical modelling of Titan's atmosphere.