On the infuence of CO on a dusty N2-CH4 CCP RF discharge

The atmosphere of Titan is mainly made of N2 and CH4. Chemical reactions, induced by solar irradiation and charged particles accelerated in Saturn's magnetosphere, lead to the production of an opaque layer of organic solid aerosols in the atmosphere. The composition and chemical production processes of these aerosols remain mainly unknown and provide a great challenge in planetary science. In order to better constrain the formation processes of these aerosols, we simulate the whole reaction chains with a laboratory Radio Frequency Capacitively Coupled plasma discharge (RF CCP) in a nitrogen and methane gas mixture. This leads to the production of laboratory analogues of Titan’s aerosols, called Tholins [1]. In this work we investigate the influence on the plasma discharge properties of carbon monoxyde (CO), the most abundant oxygenated compound in Titan's atmosphere. The experimental plasma set-up is described in details in [1] We give here the main characteristics of this experimental set up. The plasma is produced by a RF CCP discharge is confined by a metallic grounded grid. Gas are injected continuously trough the polarized electrode. Gas mixtures are adjusted with gas flow control from pure N2, premixed N2+10% CH4 and pure CO. All results presented here are obtained for a pressure of 1 mbar and 30W of injected RF power. Gaseous products are condensed in a cold trap cooled by liquid nitrogen, downstream between the plasma reactor and the vacuum pump. Then the trap is warmed up to the room temperature and connected to a Thermo Gas Chromatograph coupled with a Mass spectrometer (GC-MS). The GC-MS results show that the gas mixture is made of nitriles and hydrocarbon, as detected in a pure N2-CH4 plasma [3]. Surprisingly, no oxygenated species is detected in the gas phase, exception of carbon dioxyde CO2.