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

Abstract

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 $W.c{m}^{-3}$). 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%, pressure values between 0.5 and 4 mbar, and currents between 10 and 40 mA. The addition of less than 1% $H_2$ has a strong effect on 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: $N_2{H}^{+}$ and $N{H}_4^{+}$ being the major ones, and also $H_3^{+}$, $N{H}^{+}$, $N{H}_2^{+}$, $N{H}_3^{+}$, $N_3{H}^{+}$ and $N_3{H}_3^{+}$. 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.

Paper accepted in Plasma Sources Science and Technology in March 2023. The current version on arXiv is the accepted version. Data and codes are available at https://doi.org/10.5281/zenodo.7331908

References in corpus (3)

• N2-H2 capacitively coupled radio-frequency discharges at low pressure. Part I. Experimental results: effect of the H2 amount on electrons, positive ions and ammonia formation
• N2-H2 capacitively coupled radio-frequency discharges at low pressure. Part II. Modelling results: the relevance of plasma-surface interaction
• Interaction dust-plasma in Titan's ionosphere: feedbacks on the gas phase composition

Cited by in corpus (1)

• Interaction dust-plasma in Titan's ionosphere: feedbacks on the gas phase composition