Study of positive column of glow discharge in nitrogen by optical emission spectroscopy and numerical simulation

Nitrogen dc discharges are investigated at a constant pressure of 3 Torr and a variable discharge current of 17–100 mA. Optical emission spectroscopy is employed to detect the excited species at four axial positions far from the cathode (25, 75, 125 and 175 mm) and to determine the rotational and translational temperatures and the vibrational distribution functions (VDFs) of the B 3Πg and C 3Πu states of the nitrogen molecule. A semiempirical level-to-level collisional–radiative model is used for the modeling of the collisional and radiative processes and the processing of data. It provides detailed information on the processes occurring in the dc discharge, calculates the nitrogen emission spectra, predicts the translational and rotational temperatures, the VDFs in the ground and electronic excited B 3Πg (vB = 0–17) and C 3Πu (vC = 0–4) states together with the corresponding vibrational temperatures TV, TB and TC. Theoretical emission spectra and VDFs of the B 3Πg and C 3Πu states are also in good agreement with the experimental ones. The main processes responsible for the VDFs are also established.