Radial profiles of the emission spectra of dc glow discharge sustained in molecular gases at medium pressures

Abstract

The results of a study of the radial dependence of the emission spectra of the active dc glow discharge sustained in pure oxygen and in mixtures of CO2, N2 and He are presented. Optical emission spectroscopy has been employed to determine parameters such as rotational and vibrational temperature. Considering the CO2–N2–He mixtures, we were also able to determine the [CO]/[N2] relative concentration using the method of optical emission actinometry. The dc glow discharge in pure oxygen has been studied for pressures of 200–400 Pa and for discharge currents 20 and 40 mA. The profile was found to be flat, independent of the discharge parameters and an increase in the rotational temperature with increasing pressure and discharge current was observed. The radial profile of the vibrational temperature of nitrogen in the CO2–N2–He mixture was flat for all studied pressures (400–1330 Pa) and all discharge currents (10–40 mA). The radial profile of the [CO] relative concentration exhibited a local maximum at approximately half the radius of the discharge tube for 400 Pa. It increased uniformly from the centre to the wall of the tube at a pressure of 1330 Pa.