Metastable atomic species in the N2 flowing afterglow

Abstract

We have studied by optical emission spectroscopy the post-discharge of a pure N2 DC flowing discharge in such experimental conditions that the pink afterglow and the Lewis–Rayleigh afterglow occur. The emission profiles originated from the N2B3Πg, N2C3Πu and N2+B2Σu+ states and the N2B3Πg,6≤v≤12 and N2C3Πu,0≤v≤4 vibrational distributions were obtained in the post-discharge region. With basis on the works of Bockel et al. [S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Tech. 74 (1995) 474] and Amorim and Kiohara [J. Amorim, V. Kiohara, Chem. Phys. Lett. 385 (2004) 268], we have obtained the experimental N(4S) and N(2D) relative densities along the post-discharge. A numerical model, previously developed to describe the neutral atomic, molecular and ionic species in the afterglow, was improved to include the kinetics of N(2D) and N(2P) states. Several kinetic mechanisms leading to the production of N(2D) in the post-discharge have been studied in order to explain the experimental data. We have determined that the dominant one is the reaction N2X1Σg+,v>8+N(4S)→N2X1Σg++N(2D) with an estimated rate constant of 7×10−14cm3s−1. Also, the fit of the numerical density profiles of N2C3Πu and N2+B2Σu+ to the experimental ones has provided the rate constant for reaction N2A3Σu++N2X1∑g+,v>18→N2C3Πu+N2X1Σg+. Its estimated value is 4×10−13cm3s−1. Finally, with the new kinetic scheme, we have found that the ionization in the post-discharge region has important contribution of N(2D) and N(2P) species.