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

Abstract

We investigated flowing N 2 DC discharges both experimentally and theoretically. The discharge gas and N 2 (X 1 Σ + g) vibrational temperatures, electron density (n e), reduced electric field (E/N), and radiative state densities were measured by optical emission spectrometry (OES) and Langmuir double probes. We formulated a discharge kinetic numerical model to calculate the densities of nitrogen species as functions of the gas residence time. We combine the experimental parameters measured in the discharge with the kinetic model to analyze different discharge conditions where E/N varies significantly. First, we analyzed the measured and calculated radiative states densities and N 2 (X 1 Σ + g) vibrational distributions at the end of the positive column. Results show good agreement between calculated and measured parameters. Then, we studied the excited molecular species densities, and neutral and excited atoms densities as functions of the discharge gas residence time. This work presents for the first time the temporal densities of excited molecular and atomic states from 10 −9 to 10 −1 s discharge residence times, calculated for experimental conditions where n e presents a low variation and E/N varies from high (94 Td) to relatively low values (48 Td). The discharge experimental conditions are discharge current of 60 mA, gas pressure of 230-530 Pa, and gas flow rate of 0.9 Slm −1. Keywords Neutral and excited atoms density. Neutral and excited molecule density. Nitrogen flowing discharges

Study of ionization and ion transfer rates in flowing N2 DC discharges and post-discharges

“…Densities of N( 4 S) atoms, and N 2 (A 3 Σ + u ), N 2 (B 3 Π g ), N 2 (C 3 Π u ), and N 2 (W 3 ∆ u ) molecular states were compared to densities presented in the literature and have been found in good agreement. The N 2 (X 1 Σ + g , 0 ⩽ v ⩽ 5) states vibrational distribution functions calculated with the model were found in good agreement with experimental distributions obtained by OES [4,5,20,21]. The kinetic model accounts for 115 physical-chemical reactions between the considered species including direct impact electron excitation, dissociation, and ionization mechanisms, and excitation, deexcitation, dissociation, re-association, diffusion, ionization, and ion transfer mechanisms between atoms, molecules, and ions [4].…”

“…The second experimental set-up utilized here (B) was also employed in former studies on nitrogen flowing discharges. A detailed description of the experimental setup is presented in [4,5]. The important experimental features of these discharges arrangements are the inter-electrode distance of 12 cm, and tube diameter is 0.6 cm.…”

“…The model includes the kinetics of vibrational states of the fundamental electronic state of the nitrogen molecules N 2 (X 1 Σ + g , v) [4,5]. The species considered are:…”

“…), and N( 2 P). This kinetic model was employed in the study of molecular and atomic densities in flowing nitrogen DC discharges where the reduced electric field (E/N) varied significantly [5]. Densities of N( 4 S) atoms, and N 2 (A 3 Σ + u ), N 2 (B 3 Π g ), N 2 (C 3 Π u ), and N 2 (W 3 ∆ u ) molecular states were compared to densities presented in the literature and have been found in good agreement.…”

“…Recently, pure flowing nitrogen DC discharges were studied by OES, Langmuir double probes, and a detailed kinetic numerical model accounting for 115 physical-chemical reactions involving 18 different species of nitrogen. Densities of species and N 2 (X 1 Σ + g ) vibrational distributions (VDF) were calculated for some experimental conditions of discharges under variation of discharge electron density (n e ) and reduced electric field (E/N) [4,5].…”