Molecule formation in N and O containing plasmas
ABSTRACT The visual appearance of an expanding nitrogen plasma with or without oxygen is shown. The interaction of the plasma with a substrate leads to the appearance of additional light, which is ascribed to the formation of excited molecules by association of N and/or O atoms at the substrate.
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ABSTRACT: The dielectric-barrier (DB) discharge is an important approach to generate uniform non-equilibrium atmospheric-pressure glow discharges. We report run-to-run variations, asymmetric pulse formation and long time-scale transient phenomena in these discharges. For similar DB discharge geometric and operating conditions, we observe significant run-to-run variations as manifested in the different voltage–current waveforms at the start of each new run. These run-to-run variations are also accompanied by asymmetric pulses at the start of each run. The variations are observed to drift to a repeatable true steady-state condition on time scales of order tens of minutes to hours. Asymmetric pulse waveforms drift to a symmetric pulse waveform at the true steady state. We explore reasons for these phenomena and rule out thermal drift during a discharge run and gas-phase impurity buildup as potential causes. The most plausible explanation appears to be variations in the surface characteristics of the DBs between two consecutive runs owing to varying inter-run environmental exposure and the conditioning of the dielectric surface during a run owing to plasma–surface interactions. We speculate that the dielectric surface state affects the secondary electron emission coefficient of the surface which in turn is manifested in the discharge properties. A zero-dimensional model of the discharge is used to explore the effect of secondary electron emission.Journal of Physics D Applied Physics 05/2007; 40(10):3145. DOI:10.1088/0022-3727/40/10/018 · 2.52 Impact Factor
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ABSTRACT: The ion-molecule chemistry of the astronomically relevant H(3)(+), N(2)H(+), and NH(4)(+) ions has been investigated in the weakly ionized cold plasmas formed in glow discharges of H(2) with small amounts of nitrogen. The concentrations of neutrals and ions were determined by means of mass spectrometry, and electron temperatures and densities were measured using Langmuir probes. A kinetic model was used for the interpretation of the results. The selection of experimental conditions allowed the generation of ion distributions with different relative weights of the mentioned protonated species and the model calculations showed that the observed ion distributions can be explained by the occurrence of a very efficient H(3)(+) → N(2)H(+) → NH(4)(+) proton transfer chain. The NH(4)(+) ion, which is dominant in most of the cases studied, is ultimately derived from the small amount of NH(3) produced at the reactor walls. NH(4)(+) tends to be preponderant in the ion distributions even for NH(3) density ratios as low as 1%. Due to the high proton affinity of ammonia, this molecule is readily transformed into NH(4)(+) upon collision with H(3)(+) or N(2)H(+). It is conjectured that these results can be extrapolated to most of the small molecules predominant in the interstellar medium, which also have proton affinities lower than that of NH(3). The results support the predictions of astrochemical models indicating that NH(4)(+) could be a preponderant ion in some warm environments like hot cores, where NH(3) molecules have desorbed from the grains.Physical Chemistry Chemical Physics 12/2012; 15(5). DOI:10.1039/c2cp43438e · 4.20 Impact Factor
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ABSTRACT: The concept of physically based distributions used in studies concerning gas electrical breakdowns is introduced in this paper. The non-stationary exponential distribution of the breakdown voltages and time delays with time dependent distribution parameter is theoretically derived based on physical grounds starting from a binomial distribution for electron occurrence in the interelectrode gap. The experimental distributions of breakdown voltages Ub and time delays td are obtained by applying linearly rising (ramp) voltage pulses to the discharge tube with a hard galvanic layer of gold on the cathode and modeled by multi-component non-stationary exponential distribution, as well as by a Weibull distribution for the sake of comparison. In order to fit the experimental data, the multi-component voltage/time dependent distribution parameter YP is introduced, where Y is electron yield (number of generated electrons in the interelectrode gap per second), and P is breakdown probability (the probability of one electron to cause a breakdown). It is shown that multi-component non-stationary exponential distribution is suitable for modeling of the experimental data when time varying voltage pulses are applied to the discharge tube.Journal of Applied Physics 11/2011; 110(10):103304-103304-7. DOI:10.1063/1.3660687 · 2.19 Impact Factor