Evidence of the dominant production mechanism of ammonia in a H₂/N₂plasma

H₂/N₂ plasmas are used in a plethora of applications ranging from astrophysical comparisons to the generation of ammonia for industrial usage. Whilst the formation of ammonia is not quantitatively understood, it is widely accepted that this takes place via the progressive hydrogenation of nitrogen species at the surface through both the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Absolute ground state atomic hydrogen densities were measured, by the utilization of two-photon absorption laser induced fluorescence, in a low-pressure electron cyclotron resonance plasma as a function of nitrogen admixtures. It was observed that a secondary population of atomic hydrogen exists due to the photolysis of ammonia that was further confirmed by mass spectrometry. This nascent contribution rapidly dominates the plasma produced atomic hydrogen, with nitrogen admixtures as low as 2500 ppm, and indicates an exceptionally high nitrogen dissociation degree: a factor of 500 larger than for hydrogen. Thermally loading the reactor showed a decrease in the ammonia density for increasing temperatures, this can be explained by considering the thermally dependent recombination coefficients of the ER and LH mechanisms, from which it can be stated that the LH mechanism is dominant.