Kinetic investigation of N2 flowing DC discharges

Abstract

Nitrogen flowing DC discharges were generated between two side-armed electrodes in a drift tube. The discharges operated at gas residence times (t) of ∼4 × 10−4 s, reduced electric fields (E/N) between 90 and 118 Td, and electron densities (ne) between 1010 and 1011 cm−3. A kinetic numerical model was elaborated to study the discharge kinetics. The model calculates the densities of 18 electronic states of nitrogen in the discharge, including the 45 vibrational levels of the N2(X1Σ+g) molecules, as functions of the gas residence time. The model is employed to describe the density profiles of neutral and excited atomic and molecular species, and nitrogen ions, along with the N2(X1Σ+g) vibrational distributions for our experimental conditions. The N2(X1Σ+g) vibrational and gas temperatures, E/N, ne, and the N2(B3Πg), N2(C3Πu), and N2+(B2Σ+u) relative densities were measured in the discharge by optical emission spectroscopy and double probes. The experimental determined gas temperature (Tg), electron density, and reduced electric field were used in the calculations of the electron energy distribution function and reaction rate constants. The vibrational temperature (Tv) and excited species densities measured were compared to the calculated values from the model. Although much attention has been devoted to the study of nitrogen DC discharges in the last few years, this work presents for the first time the N+ – N4+ and N2+(B2Σ+u) ion density distribution together with the densities of 13 atomic and molecular nitrogen states as functions of the discharge gas residence time and N2(X1Σ+g) vibrational distributions calculated for experimental conditions of low pressure DC discharges operating at short residence times.

Neutral and Excited Molecules and Atoms Densities in the Positive Column of Flowing N2 DC Discharges

“…, p is the gas pressure in Torr) [9]. This procedure to obtain the electron density was utilized in several of our works on nitrogen discharges and post-discharges [8,[10][11][12][13][14][15][16][17][18]. We utilized high purity N 2 gas (99.999%) in this study.…”

“…The gas pressure gauge, flow rate meter, and the vacuum pump utilized here are the same as presented in refs. [8,18]. The discharge emissions were analyzed by a Jobin-Yvon monochromator (model 270 MST) with a grating of 1200 g mm −1 .…”

“…The kinetic numerical model accounts for reactions between the vibrational states of the electronic fundamental level of the nitrogen molecules N 2 (X 1 Σ + g , 0 ≤ v ≤ 45) and 115 physicalchemical reactions between the considered nitrogen species [8]. The VME kinetics is detailed described in refs.…”

“…They studied some excited molecular species densities for discharge residence times ranging from 4 × 10 −4 -10 −1 s for a discharge with E/N = 50 T d and n e = 8 × 10 10 cm −3 . Recently, we studied short residence time nitrogen discharges operating at different discharge currents (10-50 mA) [8]. We calculated the neutral and excited molecular and atomic densities for the experimental conditions.…”

“…The kinetic numerical model utilized here, its formulation, and specific physical-chemical reactions accounted for are detailed discussed in ref. [8]. Here, we present an analysis of positive columns from flowing nitrogen discharges under E/N variation covering the following topics: neutral and excited atoms and molecule densities, and N 2 (X 1 Σ + g ) VDFs.…”