Evolution of N-2(A(3)Sigma(+)(u)) in streamer discharges: influence of oxygen admixtures on formation of low vibrational levels

We revealed the dynamics of individual vibrational (v = 0-8) levels of N-2(A(3)Sigma(+)(u)) for various oxygen admixtures (0-20%). In pure nitrogen, the observed evolution of the N-2(A(3)Sigma(+)(u)) during the decaying streamer channel is evidence of initial vibrational relaxation of high vibrational levels towards the v = 2 and 3 levels, followed by a delayed increase of terminal (v = 0, 1) levels. A calibration procedure based on the rate of energy-pooling processes was used to place all detected vibronic levels in pure nitrogen on the absolute scale. Population maxima exceeding 1 x 10(14) cm(-3) were fixed for the v = 2 and 3 vibrational levels, while the lowest v = 0 level reaches only 3 x 10(13) cm(-3).

The formation of N-2(A(3)Sigma(+)(u)) metastable species, produced by cathode-directed streamer discharge, was investigated using the technique of laser-induced fluorescence. A triggered single streamer filament was periodically produced in pure nitrogen (and in nitrogen with admixtures of oxygen) at total pressure of 50 Torr and metastable species were monitored during the streamer channel decay in the centre of the discharge gap.