Characterization of a DC glow discharge in N_2-H_2 with electrical measurements and neutral and ion mass spectrometry

The addition of small amounts of H_2 were investigated in a DC glow discharge in N_2, at low pressure ( 1 mbar) and low power (0.05 to 0.2 W.cm^-3). We quantified the electric field, the electron density, the ammonia production and the formation of positive ions for amounts of H_2 varying between 0 and 5 between 10 and 40 mA. The addition of less than 1 the N_2 plasma discharges. Hydrogen quenches the (higher) vibrational levels of N_2 and some of its highly energetic metastable states. This leads to the increase of the discharge electric field and consequently of the average electron energy. As a result, higher quantities of radical and excited species are suspected to be produced. The addition of hydrogen also leads to the formation of new species. In particular, ammonia and hydrogen-bearing ions have been observed: N_2H^+ and NH_4^+ being the major ones, and also H_3^+, NH^+, NH_2^+, NH_3^+, N_3H^+ and N_3H_3^+. The comparison to a radiofrequency capacitively coupled plasma (RF CCP) discharge in similar experimental conditions shows that both discharges led to similar observations. The study of N_2-H_2 discharges in the laboratory in the adequate ionization conditions then gives some insights on which plasma species made of nitrogen and hydrogen could be present in the ionosphere of Titan. Here, we identified some protonated ions, which are reactive species that could participate to the erosion of organic aerosols on Titan.