Analysis of N-containing hydrocarbon species produced by a CH4/N2 microwave discharge:: Simulation of Titan's atmosphere

We report the production of gaseous hydrocarbons, nitriles, and amines in a continuous-flow microwave (MW) plasma discharge excited in a 10% CH4 + 90% N-2 mixture at a pressure of 20 torr. The product analysis was made by Li+ ion attachment mass spectrometry (Li+MS), which is suitable for identifying neutral species in the plasma, since Li+MS provides only molecular ions without any fragmentation. Since these experiments are, by design, potentially relevant to the atmospheric chemistry in Titan's stratosphere, the products were compared to those obtained from spacecraft observation and laboratory simulations. Our experiments detected more than 70 gaseous species, including 24 nitriles, 10 amines, and possibly some hydrazines. All the species found by the Voyager fly-by of Titan were detected in our simulation system. There was good agreement between our MW plasma and previous simulation experiments. These results suggest that MW discharge plasma may be a valid simulation of processes that occur in planetary atmospheres.