Nitrogen oxide γ-band emission from primary and secondary streamers in pulsed positive corona discharge

Nitrogen oxide γ-band emissions (A2 Σ+→X2 Π) from primary and secondary streamers are observed in O2/N2 and NO/N2 pulsed positive corona discharges with the aim of investigating the production of NO molecules and N2(A3 Σu+) metastables in these primary and secondary streamers. The spatial distribution of the NO-γ emission shows that the NO-γ emission is mostly observed in the secondary streamer propagation area of the O2/N2 discharge. That is, NO molecules are mainly produced in the secondary streamer in the O2/N2 discharge. On the other hand, in the NO/N2 discharge, the NO-γ emission is observed in the primary streamer propagation area. This result indicates that N2(A3 Σu+) metastables are mostly produced in the primary streamer because the NO-γ emission is observed following the process NO(X2 Π)+N2(A3 Σu+)→NO(A2 Σ+)+N2(X2 Σg), where NO(X2 Π) is distributed uniformly in the background gas in the NO/N2 discharge