Nitrile gas chemistry in Titan atmosphere

International audienceThis work presents the first study of the gaseous products resulting from the partial dissociation of methane and nitrogen in the PAMPRE experimental setup simulating Titan's atmospheric chemistry. Using cryogenic trapping, the gaseous products generated from the chemical reactions occurring in the reactor have been trapped. Analyses of these products by gas chromatography coupled with mass spectrometry have allowed the detection and identification of more than 30 reaction products. Most of them are identified as nitrile species, accompanied by aliphatic hydrocarbons and a few aromatics compounds. The observed species are in agreement with the data from the recent Cassini-Huygens mission as well as from other laboratory setups capable of dissociating nitrogen and methane. This work emphasizes the probable importance of nitrogen-bearing compounds in the chemistry taking place in Titan's atmosphere. Furthermore, a quantification of mono-nitriles with saturated alkyl chains has been performed relatively to hydrogen cyanide and shows a power-law dependence in their concentration. This dependence is consistent with the Cassini-INMS data and Titan's photochemical models. An empirical relationship has been extracted from our experimental data: [CxH2x-1N] = 100x-5 where X is the number of carbon atoms in the nitrile molecule. This relationship can be directly used in order to foretell the concentration of heavier nitriles induced by chemistry in Titan's atmosphere