Toluene removal is investigated in filamentary plasmas produced in N 2 and in N 2 /O 2 mixtures by a pulse high voltage energised DBD. Influence of the oxygen percentage (lower than 10%) and of the temperature (lower than 350°C) is examined. Toluene is removed in N 2 through collisions with electrons and nitrogen excited states. The removal efficiency is a few higher in N 2 /O 2 . It increases when the temperature increases for N 2 and N 2 /O 2 . Both H-and O-atoms play an important role in toluene removal because H can readily recombine with O to form OH, which is much more reactive with toluene than O. H follows from dissociation of toluene and of hydrogenated by-products by electron collisions. Detection of cyanhidric acid, acetylene, formaldehyde, and methyl nitrate strengthens that dissociation processes, to produce H and CH 3 , must be taken into account in kinetic analysis. Formation and treatment of deposits are also analysed.

This work is devoted to the study of atomic oxygen recombination on a glass surface, mainly in connection with atomic sources development. In this paper we present a non-stationary model for atomic oxygen recombination on a fused silica surface. Kinetics equations for oxygen atoms, taking into account heterogeneous reactions between gaseous atoms and the surface (Eley-Rideal mechanisms), as well as homogeneous processes involving surface migration of adsorbed species (Langmuir-Hinshelwood mechanisms), are solved. Surface reaction coefficients are calculated, and the choice of numerical values for surface parameters is discussed. The solution to the equations is compared to our previous experiments concerning the influence of the surface state on atomic recombination. An estimation is made of surface reaction coefficient values.

The present work is devoted to the study of the spatio-temporal distribution of the reduced electric field (REF) in a 10 ns diffuse atmospheric air discharge at very high overvoltage, in a pin-to-plane electrode geometry. The REF is derived through the intensity ratio of two wellknown transitions of molecular nitrogen: N 2 (C-B, v′=2, v″=5) and N 2 + (B-X, v′=0, v ″=0). The achieved temporal resolution is 500 ps, while the spatial resolution is better than 300 μm and 400 μm in the axial and radial direction, respectively. Due to the fast rise time of the voltage pulse, the total electric field is dramatically disturbed by the contribution of the Laplacian field, contrary to low-voltage streamer discharges. Electric field values above the ionization threshold are sustained all along the plasma channel. The dynamics of the high-voltage diffuse discharge seem similar to those of classical streamers with a very high field zone propagating towards the plane electrode then followed by a backward neutralization wave. However, some noticeable discrepancies are reported between the experimentally-obtained distributions of the axial electric field at 65 and 85 kV and those computed by means of a fluid model. They stress in particular the origin and the role of the background electrons in the discharge dynamics. Several limitations of the applicability of the intensity-ratio method for the study of very transient phenomena are also discussed. At first, the effect of the temporal integration of the signals is addressed by comparing them with an artificial averaging of the modeling results. Then, the effect of the non-stationarity of the collected signals is put forward by applying the intensityratio method under steady-state assumption or not. Lastly, the overestimation of the electric field in the discharge front due the relatively long effective lifetime of N 2 (C, v′=2) compared to the discharge dynamics is discussed.

A photo-triggered discharge has been used to study the production kinetic mechanisms and the reactivity of the hydroxyl radical in a N2/O2 mixture (5% oxygen) containing ethane or ethene for hydrocarbon concentration values in the range 1000–5000 ppm, at 460 mbar total pressure. The discharge (current pulse duration of 60 ns) has allowed the generation of a transient homogeneous non-equilibrium plasma, and the time evolution of the OH density has been measured (relative value) in the afterglow (up to 200 µs) by laser induced fluorescence (LIF). Experimental results have been explained using predictions of a self-consistent 0D discharge and plasma reactivity modelling, and reduced kinetic schemes for OH have been validated. It has been shown that recombination of H- and O-atoms, as well as reaction of O with the hydroperoxy radical HO2, plays a very important role in the production of OH radicals in the mixture with ethane. H is a key species for production of OH and HO2 radicals. As for ethane, O, H and HO2 are key species for the production of OH in the case of ethene, but carbonated radicals, following the partial oxidation of the hydrocarbon molecule by O, also play a non-negligible role. The rate constant for O- and H-atom recombination has been estimated to be 3 × 10−30 cm6 s−1 at near ambient temperature, consistent with LIF measurements on OH for both mixtures with ethane and ethene.

The time afterglow of a pulsed discharge is used to investigate the neutral-particle kinetics in N2-O2 low-pressure mixtures. The pressure is in the range 0.5-2 Torr at 300 K and the mixture composition in the range 0-20% of oxygen. Time-resolved emission spectroscopy on N2(B), N2(C), NO(A) and NO(B) is employed to monitor energy transfers involving the metastable state N2(A). The influence of N(4S) and O(3P) atoms on the kinetics is accurately treated using absolute concentration measurements by time-resolved absorption spectroscopy in the VUV range. It is shown that by an appropriate choice of the discharge repetition rate, the vibrational excitation of N2(X) can be neglected. A chemical model, containing few unknown parameters, is developed in order to fit the experimental fluorescences. The NO(X) kinetics are investigated and its absolute concentration is deduced. Furthermore, it is shown that the N2(A) density is probably higher for pulsed discharges than for stationary low-pressure DC discharges.

Pintoplane discharges in centimetre air gaps and standard conditions of pressure and temperature are generated under very high positive nanosecond scale voltage pulses. The experimental study is based on recordings of subnanosecond time resolved and Abel processed light emission profiles and their complete correlation to electrical current waveforms. The effects of the voltage pulse features (amplitude between 20 and 90 kV, rise time between 2 and 5.2 ns, and time rate between 4 and 40 kV • ns −1 ) and the electrode configuration (gap distance between 10 and 30 mm, pin radius between 10 and 200 µm, copper, molybdenum or tungsten pin material) are described. A three time period development can be found: a glowlike structure with monotonic light profiles during the first 1.5 ns whose size depends on time voltage rate, a shelllike structure with bimodal profiles whose duration and extension in space depends on rise time, and either diffuse or multichannel regime for the connection to the cathode plane according to gap distance. The transition of the light from monotonic to bimodal patterns reveals the relative effects and dynamics of streamer space charge and external laplacian field. A classical 2Dfluid model for streamer propagation has been used and adapted for very high and steep voltage pulses. It shows the formation of a strong space charge (streamer) very close to the pin, but also a continuity of emission between the pin and the streamer, and electric fields higher than the critical ionization field (28 kV • cm −1 in air) almost in the whole gap and very early in the discharge propagation.

NO removal is studied in N2/NO and in N2/NO/C2H4 mixtures through time-resolved laser-induced fluorescence in the afterglow of a pulsed homogeneous discharge. NO density measurements are compared with predictions of a 0D model on a large range of parameter values, such as the specific deposited energy and the ethene initial concentration. It is shown that dissociation of NO through collision with the N2(a′1Σu−) state play the main part in the NO removal kinetic. Moreover, quenching of N2(a′1 Σu−) by C2H4 leads to a drastic decrease of the NO removal efficiency when ethene is added to N2/NO. The determined rate coefficient value for the quenching mechanism is (4±2)×10−10 cm3 s−1.

The time post discharge of a low-pressure pulsed dc discharge in pure oxygen is used to investigate the atomic oxygen recombination on fused silica surface. With the intention of studying this recombination for different surface states, we perform before each pulsed experiment a wall treatment by means of dc discharges under different experimental conditions. Then, we monitor the decrease of the atomic oxygen in time post discharge by time resolved VUV resonant absorption spectroscopy. We have shown that it is possible to obtain for a given wall treatment, a pulse after pulse variation of this decrease. We have attributed this variation to a filling of the chemisorption sites. Finally, we have determined the surface reaction probability of atomic oxygen on fused silica surface and we have compared it to published values.