Preliminary studies for the Development of S.E.T.U.P. : "Experimental and Theoretical Simulations Useful for Planetology"

Details Preliminary studies for the Development of S.E.T.U.P. : "Experimental and Theoretical Simulations Useful for Planetology" Preliminary studies for the Development of S.E.T.U.P. : "Experimental and Theoretical Simulations Useful for Planetology"

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..440a&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

Physics

Scientific paper

This paper presents studies performed in the frame of the SETUP program (a French acronym for Experimental and Theoretical Simulations Useful for Planetology). The final goal of this project is to perform representative simulations of Titan's atmosphere and to be able to determine the physicochemical processes involved in its atmosphere. The simulation experiments will be performed in a reactor where an initial gas mixture will be exposed, for the first time, to both major energy sources (electrons and photons) that are responsible for the chemical evolution of Titan's atmosphere. Thus, the complex chemistry between N atoms and CH3, CH2, CH fragments, issued from electron dissociation of N2 and photodissociation of CH4 respectively, will be initiated. For these simulation experiments, we are planning to use a pulsed excimer KrF laser delivering photons at 248 nm to dissociate methane via a multiphotonic process because the Lyman-α radiation, mainly responsible for the dissociation of this compound in the upper atmosphere, cannot be easily reproduced in the laboratory. A first attempt to check for the energetic equivalence of the two processes - 2 photons at 248 nm vs. one single photon at Lyman-α - has already been performed and a more extensive re-examination of the methane photolysis at both wavelengths has been undertaken. The available literature indeed provides contradictory results for the methane's primary photolytic scheme at Lyman-α and no studies at all have been performed yet to establish the different photolytic decomposition pathways at 248 nm. One has to note that the available literature provides contradictory results for methane's primary photolytic scheme at Lyman-α and no studies at all have been performed yet to establish the different photolytic decomposition pathways at 248 nm. Thus, a re-examination of the methane photolysis at both wavelengths has been undertaken. Photolysis of methane has been carried out using a photochemical classic continuous lamp filled with H2/He or a KrF pulsed laser delivering radiation at 121.6 nm or 248 nm respectively In parallel of the experimental studies, a zero dimension photochemical model has been developed. It has been adapted for both studies of methane photolysis at Lyman α and 248 nm. The chemical scheme has been taken from Hebrard et al. The theoretical results have been compared to experimental ones. From this work some information about chemical mechanisms following both types of photolysis have been retrieved showing that primary products obtained at these two wavelengths are different. These results and their implication on the development of the experimental program will be presented.

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