Laboratory investigations on CH4 photochemistry in the frame of a new experimental program of Titan's atmosphere simulations
Abstract
The complex organic chemistry involved in Titan's atmosphere can be better understood via comparison between observations and results obtained by models. Unfortunately, large discrepancies have been found between theoretical and observational data concerning the mixing ratio of hydrocarbons in the stratosphere. This is probably due to inaccurate parameters used in the models and/or to lacks in the chemical schemes. A critical review of methane photochemistry will be presented first. Then, we will show new experimental projects dedicated to study methane photochemistry. Different techniques will be used to probe the photolysis fragments:
An absorption Cavity Ring Down Spectroscopy (CRDS) experiment implemented in the photolysis chamber will allow to compare the CH fragment production from two energetically equivalent photolysis processes, i.e., a single photon process at 121.6 nm (Lyman α ), and a two photon process at 248 nm. In the next future, branching ratios towards the different CH3, CH2, CH and C radicals will be determined via REMPI and fluorescence detection. Finally, we will present a new program named S.E.T.U.P, that couples laboratory experiments and theoretical studies in order to refine the theoretical description of the processes involved in Titan's atmosphere. The experimental device consists of a reactor where the initial gas mixture will be submitted, for the first time, to both major energy sources that are responsible for the chemical evolution of Titan's atmosphere: electrons and photons. Cold plasma and a UV irradiation (248 nm) will be used to dissociate N2 and CH4 (by a two photons mechanism), respectively. Time resolved analysis of the resulting gas sample will be done using spectroscopic methods. This program should provide adequate kinetic data and acurate critical reaction pathways in order to improve our knowledge of Titan complex atmospheric chemistry.- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.2771G