Measurement of vibrationally excited O₂(v= 6) in the afterglow of pulsed positive corona discharge

The density of vibrationally excited O2(v = 6) in the afterglow of a pulsed positive corona discharge is measured using time-resolved laser-induced predissociation fluorescence. Discharge occurs in a 13?mm point-to-plane gap in humid air under atmospheric pressure. When the discharge voltage is 32?kV, the O2(v = 6) density at a distance of 2.5?mm from the anode tip is 4 ? 1014?cm?3 at t = 2??s, where t is the postdischarge time, then decreases to 3 ? 1013?cm?3 by t = 15??s. The corresponding vibrational temperatures of O2, Tv, are 1400?K at t = 2??s and 1100?K at t = 15??s, which are calculated by assuming the vibrational equilibrium of O2. It is shown that the Tv of O2 in the secondary streamer channel is much higher than that in the primary streamer channel. Since the cross section of dissociative attachment (e + O2 ? O + O?) for a low electron energy (<5?eV) increases markedly with the Tv of O2, the high Tv in the secondary streamer may lead to a marked increase in O atom production in the secondary streamer in spite of its low mean electron energy (1?2?eV).