Titan organic aerosols: molecular composition and structure of laboratory analogues inferred from systematic pyrolysis gas chromatography mass spectrometry analysis

摘要

Numerous studies have been carried out to characterize the chemicalcomposition of laboratory analogues of Titan aerosols (tholins), but theirmolecular composition as well as their structure are still poorly known. Ifpyrolysis gas chromatography mass spectrometry (pyr-GCMS) has been used foryears to give clues about this composition, the highly disparate resultsobtained can be attributed to the analytical conditions used and/or todifferences in the nature of the analogues studied. In order to have a betterdescription of Titan tholins molecular composition, we led a systematicanalysis of these materials using pyr-GCMS with two major objectives: (i)exploring the analytical parameters to estimate the biases this technique caninduce and to find an optimum for analyses allowing the detection of a widerange of compounds and thus a characterization of the tholins composition ascomprehensive as possible, and (ii) highlighting the role of the CH4 ratio inthe gaseous reactive medium on the tholins molecular structure. With this aim,we used a radio-frequency plasma discharge to synthetize tholins with differentconcentrations of CH4 diluted in N2. The samples were systematically pyrolyzedfrom 200 to 600{\deg}C. The extracted gases were then analyzed by GCMS fortheir molecular identification.