Electron and metastable kinetics in the nitrogen afterglow

Abstract

This work presents a theoretical study of the time-relaxation of both the electron energy distribution function and the populations of the different species of interest in the nitrogen afterglow of a ω/2π = 433 MHz discharge at p = 3.3 Torr, in a tube with radius R = 1.9 cm. It is shown that collisions of highly excited N 2 (X 1 + g , v 35) molecules with N(4 S) atoms may be in the origin of the observed pronounced maxima for the concentrations of various species, including electrons, occurring downstream from the discharge after a dark zone. Slow electrons remain for very long times in the post-discharge (at least up to t ∼ 10 −3-10 −2 s), and the strong coupling between the electron and metastable kinetics is clearly pointed out.

Self-consistent kinetic model of the short-lived afterglow in flowing nitrogen

“…The high-sensitivity CRDS absorption technique has been used in [11] to measure the absolute density of N 2 (X, v) molecules in the v = 18 level in a dc glow discharge at p = 300 Pa and I = 100 mA. Although the level v = 18 is located in the Treanor plateau of the VDF and hence cannot be used to confirm the shape of the VDF at higher v levels, the measurement at v = 18 is in very good agreement with the present calculations [16].…”

“…This paper shows that the formation of the well-known shortlived (or pink) afterglow of nitrogen in the early flowing post-discharge can be explained as a result of near-resonant V-V energy exchange collisions leading to a pumping-up effect in the vibrational ladder. Although this fact has been already pointed out in our previous publications [14][15][16], this paper reports the final stage in these investigations in which an excellent agreement with experiment [9][10][11][12][13] has been achieved.…”

“…This work follows our previous publications [14][15][16], where we have demonstrated that the vibrationally excited molecules N 2 (X 1 + g , v), in levels as high as v > 35, should be the only energy carriers leaving the discharge capable of populating the electronic metastable N 2 (A 3 + u ) and N 2 (a 1 − u ) states in the post-discharge. This is a consequence of the well-known pumping-up effect due to near-resonant vibration-vibration (V-V) energy-exchange collisions during the vibrational relaxation of anharmonic oscillators as is the case for N 2 (X 1 + g , v) [25], CO(X 1 + , v) [26,27] and NO(X 2 r , v) molecules [28].…”

“…The set of reactions taken into account in the relaxation model for the post-discharge is basically the same as in the discharge, with the inclusion of a few new reactions. As discussed in [14][15][16], the appearance of a brightened zone downstream from the flowing discharge, in the SLA region, clearly separated by a dark zone from the power-input region, can only be explained by considering collisional processes involving highly excited vibrational levels N 2 (X 1 + g , v). In fact, due to the anharmonicity of the potential energy curve of N 2 (X 1 + g ) the V-V energy exchanges of the type…”

Evolution of Laser Plume upon Graphite Ablation in Vacuum and Nitrogen

“…Nitrogen atmosphere 5500 ± 1000 (CN) nitrogen is due to the formation, at the first steps of the "plasma life," of long-lived excited species (e.g., active nitrogen [18]) that maintain the plasma temperature via their slow relaxation.…”