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.