Speaker
Dr
Milan Simek
(Institute of Plasma Physics of the CAS, Czech Republic)
Description
We report on the N$_2$(A$^3\Sigma_u^+$, $\nu$) vibrational kinetics in nitrogen-oxygen mixtures revealed by LIF technique under DBD streamer discharge conditions at low pressures. Triggered single streamer events were produced in pure N$_2$ and N$_2$-O$_2$ mixtures employing volume DBD geometry at a pressure of 50 Torr. The discharge concept is based on a pair of metallic electrodes embedded in dielectric disks [1,2]. The discharge was powered by periodic high-voltage bursts (superimposing two sine-waves, f$_A$$_C$ = 1 kHz, with a positive pulse of a short duration of 100 ns, all applied at a fixed repetition frequency of 10 Hz). The evolution of individual vibronic levels was tracked by a modified excitation-detection LIF scheme described in detail in [2]. The LIF signal originating from the N$_2$(A$^3\Sigma_u^+$, $\nu$=0–10) vibronic levels was acquired for various delays after the streamer onset.
In pure nitrogen, the observed evolution of the LIF signal during the decaying streamer channel period evidences fast initial relaxation of high vibrational levels towards the v = 2 and 3 levels, followed by a delayed increase of terminal v = 0 and 1 levels [2]. In nitrogen-oxygen mixtures, however, the efficient quenching of higher metastable levels by oxygen significantly inhibits vibrational relaxation towards the lower and terminal levels, causing much lower populations of the v = 0–3 levels. This is already clearly visible in the N2 + 0.8% O2 mixture with vibrational kinetics limited to the first 10 microseconds of the streamer decay. In the synthetic air, the kinetics is limited only to a few microseconds in the post-discharge. We evidenced a very fast relaxation of all vibrational levels while terminal level v=0 and 1 were below the detection threshold. Furthermore, much more effective quenching of fluorescence makes the measurements extremely challenging.
Acknowledgements: Work supported by the Czech Science Foundation (GAČR no. GA15-04023S).
References:
[1] M Šimek, P F Ambrico and V Prukner, J. Phys. D: Appl. Phys. 46 (2013) 485205
[2] M Šimek, P F Ambrico and V Prukner, J. Phys. D: Appl. Phys. 48 (2015) 265202
Primary author
Dr
Milan Simek
(Institute of Plasma Physics of the CAS, Czech Republic)
Co-authors
Dr
Paolo Ambrico
(CNR NANOTEC)
Dr
Václav Prukner
(Institute of Plasma Physics v.v.i.)
