N₂ dissociation and kinetics of N(⁴S) atoms in nitrogen DC glow discharge

Abstract

N2 dissociation in pure nitrogen plasma has a long history of research. It seems to be a complex process which comprises many reactions involving various electronic and vibrational nitrogen states whose contributions can vary depending on conditions. In this paper, we studied N2 dissociation in the stationary N2 discharge both experimentally and theoretically. We used a DC glow discharge in a quartz tube in pure N2 at moderate pressures (5–50 Torr). The degree of dissociation, atomic nitrogen loss rate and gas temperature were measured by applying optical emission spectroscopy (OES) and as a result an ‘effective’ rate constant for nitrogen dissociation was obtained across a wide range of the reduced field E/N. The analysis of N2 dissociation was carried out using a specially developed 1D radial self-consistent model which takes into account the spatial inhomogeneities of species concentrations, E/N, electron energy distribution function, Tgas etc, together with fairly complete plasma-chemical kinetics and all the cross-sections known to date for electron kinetics. The model was successfully validated through the experimental results obtained for electric field, gas temperature and N atom density. Comprehensive analysis of closely coupled processes in nitrogen plasmas—gas heating, VDF formation and N2 dissociation—was carried out. Simulations reproduced the experimental data on well and allowed us to evaluate the different contributions of the various dissociation channels considered. It was shown that the nitrogen dissociation mechanism in the stationary N2 discharge is provided by direct electron impact via the excitation of the pre-dissociative states from the vibrationally excited nitrogen molecules N2(X, υ). The upper limit for the rate constant of the processes N2(A) + N2(14 ⩽ υ ⩽ 19) → N + N + N2 was estimated to be 5 · 10−14 cm3 s−1.

Does the energy transfer from Ar(1s) atoms to N2 lead to dissociation?

“…[4] A large fraction of the energy dissipated in N 2 plasmas at reduced fields, typical of DBDs, goes into vibrationally excited states. [5] Adverse consequences are comparably high voltages necessary to drive N 2 DBDs and excessive (vibrational) heating of the gas.…”

N-Doped Carbon NanoWalls for Power Sources

“…Discharge current density at the cathode (j~0.4 mA cm −2 ) and measured cathode temperature T c = 310 K hints at an abnormal regime of the discharge operation. Based on plasma-chemical and electron kinetics calculations of N 2 plasma 24 we estimate the electron and ion concentration n e ≈ n i ~10 8 cm −3 , reduced electric field E/N~55 T d and respective electron temperature T e ~1 eV in positive column between the cathode and sample surfaces. In these conditions, N atoms in ground N( 4 S) and lowest metastable N( 2 D) and N( 2 P) states are effectively produced in N 2 dissociation by electron impacts.…”

Absolute N-atom density measurement in an Ar/N2 micro-hollow cathode discharge jet by means of ns-two-photon absorption laser-induced fluorescence

“…The measured N atoms density was higher than those obtained in all Ar/N 2 mixtures. In pure nitrogen, it has been shown that the production of N atoms may occur through several processes which can be summed up in two categories: dissociation of the ground state molecules (at different vibrational levels, v) N 2 (X 1 Σ + g , v) by electron impact, and collisions of N 2 molecules that are excited in various electronic and vibrational states 44 . While it is difficult to estimate the dominant dissociative processes in our case, since we are not aware of the existence of an extensive model of our peculiar discharge in nitrogen, it is possible that Ar atoms are not completely detrimental to a nitrogen discharge.…”