Role of long-lived N₂(X¹Σ_g⁺,v) molecules and N₂(A³Σ_u⁺) and N₂(a'¹Σ_u^-) states in the light emissions of an N₂afterglow

Abstract

The enhancement of N 2 (B 3 g) and N + 2 (B 2 + u) states, responsible by the emission bands for the 1 + and 1 − systems of N 2 , in the short-lived afterglow of a flowing N 2 microwave discharge at ω/(2π) = 433 MHz is investigated by modelling. It is shown that pronounced maxima for both emissions are obtained downstream from the discharge by assuming the formation of N 2 (A 3 + u) and N 2 (a 1 − u) states by collisions of N 2 (X 1 + g , v) molecules in highly vibrational levels with N(4 S) atoms. Other channels that can also produce the emissions are investigated as well, but the common factor in all of them is the role played by the vibrationally excited N 2 (X,v) molecules in levels >35. During the relaxation process a pumping-up effect for the vibrational quanta at the higher vth levels occurs as a result of near-resonant V-V energy-exchange collisions, that produces a rise in the observed peaks for the N 2 electronic states in the flowing afterglow.

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

“…These discharges are used for steel surface nitriding [1], thin-film deposition [2,3], plasma assisted pulsed laser deposition [4], metal surface cleaning [5] and, more recently, in bacterial sterilization [6,7]. Accordingly, a large number of both experimental [8][9][10][11][12][13] and theoretical [14][15][16] works have appeared in the literature with the aim of getting a deeper insight into the understanding of the kinetics of long-lived species in these non-equilibrium media: vibrationally excited ground-electronic state N 2 (X 1 + g , v) and metastable N 2 (A 3 + u ) molecules, and ground-state N( 4 S) and metastable N( 2 D, 2 P) atoms. Once these species are created in the discharge region of a flowing N 2 microwave [14][15][16] or dc discharge [17], they may be either carried out to the postdischarge or created again in the post-discharge, as a result of a complex interplay kinetics involving other species.…”

Active nitrogen and oxygen: Enhanced emissions and chemical reactions

“…(8) that involves reaction of O 2 (a 1 D g ) with highly vibrationally excited N 2 ðX 1 R þ g Þ states certainly does also conserve spin, since two singlet species may give rise to two triplet species. However, the concentration of the vibrational N 2 states is reported [68,69] to be comparable to, or even higher than that of N( 4 S) atoms, for at least up to m = 30. Therefore, their rate of participation in the quenching of O 2 (a 1 D g ) is equal to, or slower than that reported for N( 4 S) atoms.…”

Detection of metastable excited molecules N2(A3Σu+) in an atmospheric pressure nitrogen discharge by Raman scattering

“…Modeling based on pure calculations without using optical emission data has also been performed [18][19][20], but these focus on the low-pressure regions commonly used in plasma processes. For discharges at atmospheric pressure, thermal fluid models have been reported [21], but do not include discussion at the molecular level, taking into account the effects of excitation levels.…”