Evolution of N2(A3Σ+u) in streamer discharges: influence of oxygen admixtures on formation of low vibrational levels.

0483130 - ÚFP 2018 RIV GB eng J - Journal Article
Šimek, Milan - Ambrico, P. F. - Prukner, Václav
Evolution of N2(A3Σ+u) in streamer discharges: influence of oxygen admixtures on formation of low vibrational levels.
Journal of Physics D-Applied Physics. Roč. 50, č. 50 (2017), č. článku 504002. ISSN 0022-3727. E-ISSN 1361-6463
R&D Projects: GA ČR(CZ) GA15-04023S
Institutional support: RVO:61389021
Keywords : nitrogen * air * streamer * laser-induced fluorescence * LIF
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 2.373, year: 2017
http://iopscience.iop.org/article/10.1088/1361-6463/aa96f3

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.
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).
Populations of v = 2-5 vibrational levels were also estimated for N-2 + O-2 mixtures after scaling of laser-induced fluorescence signals obtained at various oxygen admixtures. The total N-2(A(3)Sigma(+)(u)) population in an air-like mixture is formed mainly by v = 3-4 vibronic levels with the population maximum of similar to 3 x 10(13) cm(-3) fixed at the shortest analyzed delay. This observation, together with the fact that we were unable to detect v = 0 and 1 levels (fluorescence signals below detection threshold), gives a strong evidence of the inhibition of Delta v = 2 vibrational relaxation towards terminal v = 0 and 1 levels, causing much lower populations of the lowest v = 0-1 levels.

Permanent Link: http://hdl.handle.net/11104/0278536