Study of rotational temperature of oxygen molecules in H and T forms of DC glow discharge sustained in pure oxygen

The active DC glow discharge sustained in pure oxygen has been studied in a Silica discharge tube by means of optical emission spectroscopy and double-probe diagnostics for pressures 600, 750 and 1000 Pa and for discharge currents up to 40 mA. Two different forms of positive column of the discharge (high-gradient H form and low-gradient T form) were observed. Our investigation was focused on the variations of the rotational temperature T rot determined from emission spectra of molecular oxygen (atmospheric A-band at 760 nm) in the dependence on the discharge current and on the pressure with respect to the existence of the two forms of the discharge. An increase of the rotational temperature with increasing discharge current has been observed. Moreover, higher values of T rot were found in the H form compared with the T form. ► T and H forms of oxygen discharge were observed for 750 and 1000 Pa. ► T form does not hold decrease of the electric field strength with increasing current. ► The rotational temperature of oxygen molecules increases with discharge current. ► The rotational temperature is higher in the H form compared to the T form.