Effect of controlled O2 impurities on N2 afterglows of RF discharges

A RF capacitive flowing discharge and post-discharge are experimentally studied in N2 gas and N2-(10−4–10−2)O2 gas mixtures by using the optical emission spectroscopy at a pressure of 8 Torr, a flow rate of 1 slm and a transmitted RF power of 100 W. In these conditions the flowing discharge is distinguished by early and late afterglow. It is shown that the early afterglow is very sensitive to small quantity of O2. The band emissions from N2+(B) and N2(B,υ′) decreased sharply in the early afterglow when O2 is introduced before the plasma. By using simple gas kinetics for pseudo-stationary conditions in the afterglows, N2++O2 charge transfer and N2(a′) quenching by O2 play key roles in the afterglow. The charge transfers and quenching reactions are amplified when O-atoms are produced in the plasma. It is also observed that the O-atoms are produced in the early afterglow when O2 is introduced after the plasma. ► A capacitive flowing post-discharge has been experimented in N2–O2 gas mixture. ► We found that the pink afterglow is sensitive to O2 as soon as 0.01% O2 is into N2. ► The N2+ 391.4 nm band decreased sharply as the results of N2++O2 charge transfer. ► The charge transfers is amplified when O-atoms are produced in the plasma.