Effect of controlled O2 impurities on N2 afterglows of RF discharges

A RF capacitive flowing discharge and post-discharge are experimentally studied in N-2 gas and N-2-(10(-4) -10(-2))O-2 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 O-2. The band emissions from N-2(+)(B) and N-2(B,upsilon') decreased sharply in the early afterglow when O-2 is introduced before the plasma. By using simple gas kinetics for pseudo-stationary conditions in the afterglows, N-2(+) + O-2 charge transfer and N-2(a') quenching by O-2 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 O-2 is introduced after the plasma. (C) 2012 Elsevier B.V. All rights reserved.