Kinetic modeling of low-pressure nitrogen discharges and post-discharges

Abstract

The kinetic modeling of low-pressure ($p\sim 1{-}10$ torr) stationary nitrogen discharges and the corresponding afterglows is reviewed. It is shown that a good description of the overall behavior of nitrogen plasmas requires a deep understanding of the coupling between different kinetics. The central role is played by ground-state vibrationally excited molecules, N₂$(X\ ^1\Sigma_g^+,v)$, which have a strong influence on the shape of the electron energy distribution function, on the creation and destruction of electronically excited states, on the gas heating, dissociation and on afterglow emissions. N₂$(X\ ^1\Sigma_g^+,v)$ molecules are actually the hinge ensuring a strong link between the various kinetics. The noticeable task done by electronically excited metastable molecules, in particular N₂$(A\ ^3\Sigma_u^+)$ and N₂$(a^\prime\ ^1\Sigma_u^-)$, is also pointed out. Besides contributing to the same phenomena as vibrationally excited molecules, these electronic metastable states play also a categorical role in ionization. Furthermore, vibrationally excited molecules in high v levels are in the origin of the peaks observed in the flowing afterglow for the concentrations of several species, such as N₂$(A\ ^3\Sigma_g^+)$, N₂$(B\ ^3\Pi_g)$, N₂⁺$(B\ ^2\Sigma_u^+)$ and electrons, which occur downstream from the discharge after a dark zone as a consequence of the V-V pumping-up mechanism.