Evolution of N-2(A(3)Sigma(+)(u)) in streamer discharges: influence of oxygen admixtures on formation of low vibrational levels. Simek, M., Ambrico, P. F., & Prukner, V. JOURNAL OF PHYSICS D-APPLIED PHYSICS, DEC 20, 2017.
doi  abstract   bibtex   
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. By analyzing data obtained in pure nitrogen and in nitrogen with three different oxygen admixtures, we have estimated the quenching rate constants of N-2(A(3)Sigma(+)(u), v) + O-2 and N-2(A(3)Sigma(+)(u), v) + N-2 processes for v = 2-6 vibrational levels which are consistent with data from the literature. Quenching rate constants for nitrogen reflect the N-2(A(3)Sigma(+)(u), v) -> N-2(A(3)Sigma(+)(u), v-2) relaxation process, however the v = 2 rate constant shows a much larger value compared with the published data.
@article{ ISI:000416005900001,
Author = {Simek, M. and Ambrico, P. F. and Prukner, V.},
Title = {{Evolution of N-2(A(3)Sigma(+)(u)) in streamer discharges: influence of
   oxygen admixtures on formation of low vibrational levels}},
Journal = {{JOURNAL OF PHYSICS D-APPLIED PHYSICS}},
Year = {{2017}},
Volume = {{50}},
Number = {{50}},
Month = {{DEC 20}},
Abstract = {{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.
   By analyzing data obtained in pure nitrogen and in nitrogen with three
   different oxygen admixtures, we have estimated the quenching rate
   constants of N-2(A(3)Sigma(+)(u), v) + O-2 and N-2(A(3)Sigma(+)(u), v) +
   N-2 processes for v = 2-6 vibrational levels which are consistent with
   data from the literature. Quenching rate constants for nitrogen reflect
   the N-2(A(3)Sigma(+)(u), v) -> N-2(A(3)Sigma(+)(u), v-2) relaxation
   process, however the v = 2 rate constant shows a much larger value
   compared with the published data.}},
DOI = {{10.1088/1361-6463/aa96f3}},
Article-Number = {{504002}},
ISSN = {{0022-3727}},
EISSN = {{1361-6463}},
ResearcherID-Numbers = {{Simek, Milan/E-6941-2014}},
ORCID-Numbers = {{Simek, Milan/0000-0003-1730-8493}},
Unique-ID = {{ISI:000416005900001}},
}
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