LIF diagnostics of hydroxyl radical in atmospheric pressure He-H2O dielectric barrier discharges (original) (raw)
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Applied Physics Express, 2011
The OH radical density and gas temperature in atmospheric pressure glow discharges with a liquid cathode or anode is measured with a laserinduced fluorescence (LIF) technique exciting the P 2 (3), Q 1 (4), and Q 1 (9) branches of the X 2 Å, 00 ¼ 0-A 2 AE, 0 ¼ 3 transition. Glow discharge in contact with liquid is generated by positive and negative voltages at currents of 10-28.5 mA. The density of OH radicals linearly increases from 1:32 Â 10 21 (water anode) and 1:3 Â 10 21 m À3 (water cathode) to 8:95 Â 10 21 and 1:78 Â 10 22 m À3 , respectively, with the increase of the discharge current from 10 to 28.5 mA. #
Observation of OH radicals produced by pulsed discharges on the surface of a liquid
Plasma Sources Science and Technology, 2011
The hydroxyl radical (OH) plays an important role in plasma chemistry at atmospheric pressure. OH radicals have a higher oxidation potential compared with other oxidative species such as free radical O, atomic oxygen, hydroperoxyl radical (HO 2 ), hydrogen peroxide(H 2 O 2 ) and ozone. In this study, surface discharges on liquids (water and its solutions) were investigated experimentally. A pulsed streamer discharge was generated on the liquid surface using a point-to-plane electrode geometry. The primary generation process of OH radicals is closely related to the streamer propagation, and the subsequent secondary process after the discharge has an influence on the chemical reaction. Taking into account the timescale of these processes, we investigated the behavior of OH radicals using two different diagnostic methods. Time evolution of the ground-state OH radicals above the liquid surface after the discharge was observed by a laser-induced fluorescence (LIF) technique. In order to observe the ground-state OH, an OH [A 2 + (v = 1) ← X 2 (v = 0)] system at 282 nm was used. As the secondary process, a portion of OH radicals diffused from gas phase to the liquid surface and dissolved in the liquid. These dissolved OH radicals were measured by a chemical probe method. Terephthalic acid was used as an OH radical trap and fluorescence of the resulting 2-hydroxyterephthalic acid was measured. This paper directly presents visualization of OH radicals over the liquid surface by means of LIF, and indirectly describes OH radicals dissolved in water by means of a chemical method.
The European Physical Journal D, 2009
Simultaneous measurements of absolute concentrations of H2O and OH radicals in an atmospheric AC discharge using continuous wave cavity ringdown spectroscopy (cw-CRDS) are reported. Formation of OH radicals and plasma temperatures are characterized by optical emission spectroscopy. The concentration of OH radical at the edge of the discharge plume at 380 K is measured by the cw-CRDS technique to be 1.1×10 15 molecule cm −3 . Ringdown measurements of the H2O (120-000) band and the OH first overtone around 1515 nm enable us to determine an OH generation yield, Φ = N OH N H 2 O , to be 4.8 × 10 −3 , where NOH and NH 2 O are the number densities of OH and H2O, respectively. The minimum detectable absorption coefficient of the cw-CRDS system is 8.9 × 10 −9 cm −1 , which corresponds to a 1σ detection limit of OH number density of 1.2 × 10 13 molecule cm −3 in the discharge. This experimental approach is demonstrated for the first time ever in an AC discharge, and can be applied in general to a variety of atmospheric plasmas to help study OH formation mechanisms and OH-related plasma applications.
Journal of Physics D: Applied Physics, 2012
The density of OH radicals in ground state is measured by laser-induced fluorescence (LIF) spectroscopy in the core of a micro-flow discharge in He, Ar and N 2 with a water electrode. The lines P 2 (6), P 1 (4) and P 2 (3) of the X 2 (v = 0) to the A 2 + (v = 1) transition are used for OH radical excitation. The density of the main quencher of OH radical in the core of the discharge is estimated based on the time decay of the LIF signal. It is revealed that the plasma core consists of a high amount of 8-10% of water vapour. The calculation of the absolute density of OH radical is carried out based on the model of LIF excitation including vibrational and translation energy transfer, and the results in different gases are presented for the discharge.
Journal of Physics D Applied Physics
The density of OH radicals in ground state is measured by laser-induced fluorescence (LIF) spectroscopy in the core of a micro-flow discharge in He, Ar and N2 with a water electrode. The lines P2(6), P1(4) and P2(3) of the X 2� (v �� = 0) to the A2+ (v� = 1) transition are used for OH radical excitation. The density of the main quencher of OH radical in the core of the discharge is estimated based on the time decay of the LIF signal. It is revealed that the plasma core consists of a high amount of 8–10% of water vapour. The calculation of the absolute density of OH radical is carried out based on the model of LIF excitation including vibrational and translation energy transfer, and the results in different gases are presented for the discharge.
IEEE Transactions on Plasma Science, 2014
It has been proven that many types of radicals released from atmospheric-pressure plasma can provide effective surface treatment and modification of materials. However, the method for measuring radicals generated with atmosphericpressure plasma and their reaction mechanisms have not become clear in material surface processing. The OH radical distribution was measured successfully in nonequilibrium atmospheric-pressure dc pulse discharge plasma jet by use of the laser-induced fluorescence system. The OH transition [ A 2 + (v = 1) ← X 2 (v = 0)] at 282 nm was used to monitor the ground-state OH radicals.
J Phys D Appl Phys, 2010
In this paper we report on a spectroscopic study on CH observables including laser induced fluorescence (LIF) on CH and emission spectroscopy on the CH Gerö band. Direct observation by LIF has been found to be very difficult, both because of technical difficulties and an overall low CH density in the discharge. Analysis of CH(A) emission shows that it is due to CH 4 dissociative excitation processes, by He(2 3 S) in He-based mixtures, and by electron impact in N 2 -CH 4 . The analysis of spectra evidences the need for more precise knowledge on the collision quenching of electronically excited states and on the electron energy distribution function.
Review of Scientific Instruments, 1994
The odd-hydrogen radicals OH and HO2 are central to most of the gas-phase chemical transformations that occur in the atmosphere. Of particular interest is the role that these species play in controlling the concentration of stratospheric ozone. This paper describes an instrument that measures both of these species at volume mixing ratios below one part in lOI in the upper troposphere and lower stratosphere. The hydroxyl radical (OH) is measured by laser induced fluorescence at 309 nm. Tunable UV light is used to pump OH to the first electronic state (A 2~+(u"l) c x2n 3,2 (u"= 0)) near 282 nm. The laser light is produced by a high-repetition rate pulsed dye-laser powered with all solid-state pump lasers. HO:! is measured as OH after gas-phase titration with nitric oxide. Measurements aboard a NASA ER-2 aircraft demonstrate the capability of this instrument to perform reliably with very high signal-to-noise ratios (>30) achieved in short integration times (< 20 set).