Mass spectrometric analysis of small negative ions (e/m < 100) produced by Trichel pulse negative corona discharge fed by ozonised air

Mass spectrometric analysis of small negative ions (e/m < 100) produced by DC negative corona discharge in ozonised wet air both in flow and flow-stopped regimes was conducted at pressure of 30 kPa. The point-to-plain electrode system has been used. The yield of individual ions is strongly affected by trace concentrations of ozone in both regimes. Ozone concentration greater than 25 ppm is sufficient to completely suppress the appearance of O2- and a NO2- ion as well as theirs clusters in the mass spectra. The temporal increase in concentration of NO3- ions and NO3-.(H2O)n (n = 1, 2) hydrated clusters was observed in flow-stopped regime accompanied by reduction in yield of CO3- ion and its water clusters CO3-.(H2O)n (n = 1, 2), which otherwise are the dominant ions in flowing wet air free of ozone. In contrast the addition of ozone into the flow of wet air resulted in evident increase in abundance of the clusters CO3-.(H2O)n (n = 1, 2). This is an evidence of an active role of nitrous oxide produced in flow-stopped regime in sufficient amount. The measured electrical conductivity of drift region confirmed the role of additional dissociative attachment of electrons by ozone molecules as well as a formation of clusters of lower mobility with increasing ozone concentration in the discharge gap

Spectra of Ions Produced by Corona Discharges

A mass spectrometric study of ions extracted from both positive and negative DC corona discharges, initiated in point-to plane electrode system, has been carried out in ambient air at low air pressure (5 – 30) kPa. The average relative humidity of air was typically 40–50 %. Ions were extracted through a small orifice in the plane electrode into an intermediate gap where the low pressure prevented further ion-molecule reactions. Mass analysis of negative ions formed in the negative corona discharge using ambient air has shown that the yield of individual ions is strongly affected by trace concentrations of ozone, nitrogen oxides, carbon dioxide and water vapour. In dry air the CO3− ion was found to be dominant. In presence of water this is converted very efficiently to cluster ions CO3−·(H2O)n containing one and more water molecules. The yield of O3−·(H2O)n clusters or core ions was found to be considerably lower than in some other studies at atmospheric pressure. The mass spectrum of ions extracted from drift region of a positive corona discharge was simpler being dominantly cluster ions H3O+·(H2O)n most probably formed from O2+ ions, a two step process being active if water molecules are present in the discharge gap even at relatively low concentration

A Study of the Physical and Chemical Processes Active in Ozone Generation by Carbon Dioxide Fed Corona Discharges

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO2 has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O2 and N2+O2 mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O3] was observed at decreasing oxygen content in mixtures and the constant input energy density . The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O3] = f() with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N2+O2 mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O2 mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation

Low energy electron attachment to SF5CF3

Low energy electron attachment to the potent greenhouse gas SF5CF3 is studied at high energy resolution by means of mass spectrometric detection of the product anions. A large dissociative electron attachment (DA) cross-section forming SF5−+CF3 is observed within a very narrow energy range close to zero eV. In addition, comparatively weak resonances are observed near 1 eV yielding the fragment ions CF3− and F−. Some implications for the atmospheric lifetime of SF5CF3 and hence its global warming potential (GWP) are considered

Dissociative electron attachment to dinitrogen pentoxide, N2O5

Electron attachment was studied in gaseous dinitrogen pentoxide, N2O5, for incident electron energies between a few meV and 10 eV. No stable parent anion N2O5- was observed but several anionic fragments (NO3-, NO2-, NO-, O-, and O-2(-)) were detected using quadrupole mass spectrometry. Many of these dissociative pathways were found to be coupled and provide detailed information on the dynamics of N2O5 fragmentation. Estimates of the cross sections for production of each of the anionic fragments were made and suggest that electron attachment to N2O5 is amongst the most efficient attachment reactions recorded for nonhalogenated polyatomic systems. (C) 2004 American Institute of Physics