Three-body Electron Attachment Research Articles

Two- and three-body attachment, electron transport and ionisation in water-air mixtures

Three-body electron attachment in the mixtures of H2O and dry air have been measured over a wide range of the density-reduced electric field, E/N, from 3–130 Td and gas pressures, for mixture combinations ranging from 1% to 50% of H2O. We have measured the regions of three-body attachment (3–30 Td) and two-body dissociative attachment (40–130 Td). Besides, the increasing amount of H2O in the mixture causes an increase in the three-body reaction rates of up to two orders of magnitude in comparison with that measured for dry air. On the other hand, the three-body attachment coefficients exceed the two-body ones (dissociative attachment) at high pressures. Good agreement has been found with previous measurements of H2O-dry air mixtures with H2O concentrations of up to 2%. We know of no previous work for higher H2O concentrations. Values of the effective ionisation coefficients and longitudinal diffusion coefficients derived from the same measurements are also presented.

The influence of humidity on positive streamer propagation in long air gap

A 2D numerical simulation of the positive streamer properties was performed in 9–12 cm plane-to-plane air gaps for various pressures and water vapor contents. It was shown that an increase in air humidity leads to hampering the streamer development and to increasing the average critical electric field required for bridging the discharge gap. The effect of humidity was most profound at atmospheric pressure and decreased with decreasing pressure. The influence of water content on the streamer properties was explained by a decrease in the streamer channel conductivity due to dissociative recombination of electrons with positive hydrated ions and enhanced three-body electron attachment to O2 molecules. The calculated critical electric field and streamer velocity in humid air gaps were compared with available experimental data.

Three-dimensional simulation of ionic wind in a laminar premixed Bunsen flame subjected to a transverse DC electric field

The role of the ionic wind effects on modifying flame dynamics was demonstrated by detailed computational models. Full three-dimensional simulations were conducted to reproduce and describe the response of a laminar premixed methane–air Bunsen flame subjected to a transverse DC electric field at saturation condition. The chemical kinetic mechanism employed a methane–air skeletal mechanism with an optimized ionization model to predict the positive and negative ions that are important for generating the electric currents. Given the strong dependence of the ionic wind on the amount of charged species created by chemi-ionization, the ion production rate was optimized to match the measured saturation current. The simulation successfully reproduced the flame tilt toward the cathode. The ionic winds blowing from the flame toward the electrodes in both rightward and leftward directions were also captured. The calculated flow field is qualitatively consistent with the PIV experimental data. Accurate description of the three-body electron attachment to oxygen and the charge transfer reactions generating heavy anions was found to be critical in simulating the flame–electric field interaction. This is a first demonstration of the ionic wind effect by full three-dimensional simulations. Further investigation by both experiment and modeling are required in future work to address quantitative differences.

Simulation of pulsed positive streamer discharges in air at high temperatures

Two-dimensional simulations of an atmospheric-pressure streamer discharge at high gas temperatures were performed in humid air at initial gas temperatures, T0, in the range 300 K–600 K with the same electrode and applied voltage conditions as those used in Ono and Kamakura (2016 Plasma Sources Sci. Technol. 25 044007). The simulation was validated by comparing its results to experimentally obtained discharge currents, primary streamer velocities, and secondary streamer diameters and lengths. This paper discusses the mechanisms underlying the temperature effects in terms of the behaviour of the charged particles in the primary and secondary streamers. At T0 = 300 K, the main decay processes in the primary streamer are the electron recombination reactions with cluster ions and electron three-body electron attachment with O2 and H2O, while the main decay process in the secondary streamer is the two-body electron attachment to O2. Although, at T0 = 600 K, the main decay processes in both streamers are still recombination and two- and three-body electron attachment reactions, the rates of these reactions decrease owing to the increase in the gas temperature, which leads to the increased conductivity of streamer discharge channels at high gas temperatures.

Electron attachment to oxygen in nitrogen buffer gas at atmospheric pressure

We have carried out experimental and theoretical studies of three body electron attachment (TBEA) to O2 in N2/O2 mixtures. We have applied three different experimental methods to determine the apparent rate constant k for TBEA to O2 for reduced electric fields E/ n from 0.5 Td up to 4.5 Td and O2 concentrations from 0.02% up to 3%. From the apparent rate constant k we have evaluated three body rate constant for electron attachment to O2 in pure O2 $$\left( {k_{O_2 } } \right)$$ and in pure N2 $$\left( {k_{N_2 } } \right)$$ . The comparison of present data with former studies shows that the former values of $$k_{N_2 }$$ overestimated the efficiency of this reaction, while in case of $$k_{O_2 }$$ we have found agreement with earlier studies. We have solved numerically the Boltzmann equation of the electrons and calculated the values of k, $$k_{N_2 }$$ and $$k_{O_2 }$$ using well established cross sections. Using the known collision cross section set for TBEA to O2, very good agreement between calculated and measured results for $$k_{O_2 }$$ was found, while in the case of k and $$k_{N_2 }$$ we had to introduce a scaling function, which describes the decrease of the efficiency of TBEA to O2 in presence of N2 and the dependence of the scaling function on E/n was determined.

Direct measurement of the characteristic three-body electron attachment time in the atmospheric air in direct current electric field

We report the results of theoretical and experimental study of the characteristic time for three-body attachment of electrons produced by 100 fs UV laser pulse in the atmosphere air in the external DC electric field ranged from 0.2 to 10 kV/cm.

Low-energy electron attachment and detachment in vibrationally excited oxygen

Three-body electron attachment to O2 molecules and electron detachment from ions have been theoretically studied in vibrationally excited oxygen and O2-containing mixtures. Assuming that electron attachment and detachment proceed via the formation of vibrationally excited temporary ions, the rates of these processes were determined on the basis of the statistical approach for the vibrational transfer and relaxation in collisions between ions and O2 molecules. The calculated attachment and detachment rate constants turned out to agree well with available measurements in unexcited oxygen. This method was extended to calculate attachment and detachment rates in vibrationally excited oxygen. It was shown that the effect of vibrational excitation on electron detachment is profound, whereas attachment of low-energy electrons to vibrationally excited O2 is inefficient. The calculated vibrational distribution of stable ions turned out to be non-equilibrium in an excited gas and the effective vibrational temperature of the ions was much lower than the vibrational temperature of molecules. An analytical method was suggested to determine this distribution and the effective vibrational temperature. The calculated rate constants were used to simulate the formation and decay of an electron-beam-generated plasma in N2 : O2 mixtures at elevated vibrational temperatures. The calculations showed that vibrational excitation of molecules leads to orders of magnitude increase in the plasma density and in the plasma lifetime, in agreement with available observations.

Mitigation of electron attachment to oxygen in high pressure air plasmas by vibrational excitation

A series of time resolved microwave attenuation measurements are performed of the electron number density of an electron beam generated, CO laser excited nonequilibrium O2∕N2 plasma. Resonant absorption of infrared radiation from the CO laser produces the nonequilibrium state, in which the heavy species vibrational modes are disproportionately excited, compared to the rotational and translational modes (Tvib≈2000–3000K vs TR∕T≈300K). It is shown that this results in an increase in the plasma free electron lifetime by two orders of magnitude compared to the unexcited cold gas, an effect which is ascribed to complete mitigation of rapid three-body electron attachment to molecular oxygen. A series of heavy species filtered pure rotational Raman scattering measurements are also presented, which exhibit minimal temperature change (+50K), indicating that the observed lifetime increase cannot be due to heavy-species thermal effects. Finally, computational modeling results infer an increase in the rate of O2− detachment by four to five orders of magnitude, compared to the equilibrium value.

A multi-species DC stationary model for negative corona discharge in oxygen; point-plane configuration

This paper analyzes the steady-state model of negative corona discharge in pure oxygen at room temperature and under atmospheric pressure assuming the point-plane geometry. Three species of charge carriers: electrons, negative oxygen ions O 2 - and positive oxygen ions O 2 + ions, are assumed. Five different ionic reactions for the corona discharge are studied, including electron impact ionization, three-body attachment of electrons to oxygen molecules, three-body recombination of electrons and positive oxygen ions, three-body recombination of negative and positive oxygen ions, and two-body recombination of negative and positive oxygen ions. The simulation results show the electron, negative and positive oxygen ion densities along the axial direction, lines of equal charge density for these three species in the air gap, and electric field distribution along the axis of symmetry.

1080 PUBLICATION Surgical treatment craniofacial malignant tumors

The combustion of methanol was studied in a conical methanol—oxygen flame of fuel-lean composition (equivalence ratio φ = 0.25) burning at atmospheric pressure surrounded by a flowing argon shield. Oxygen bubbled through liquid methanol contained in two gas saturators provided a premixed flame of excellent stability and reproducibility. The flame gas was sampled into a mass spectrometer which was used to detect a variety of naturally occurring ionic species, both positive and negative. Although the maximum level of ionization in this flame had the rather low value of 5 × 108 ions ml−1, nevertheless concentration profiles were drawn as a function of distance along the flame axis at 17 individual mass numbers (m/z) for positive ions and 11 for negative ions; that is, whenever an appreciable signal could be detected below 100 amu. The positive profiles in the reaction zone are dominated by proton transfer processes which indicate that CHO+ is the primary ion. A variety of protonated combustion intermediates and products were detected including both stable molecules (H2O, HCHO, the CH3OH fuel, CH2CO, CH3CHO, HCOOH and possibly CH3OCH3/C2H5OH) and radicals (C, CH, CH2, HCO, CH2OH or CH3O, CH3CO or CH2CHO, and possibly CH3OO). Chemical ionization by charge transfer is certainly operative for two species (O2 and NO as an impurity) and perhaps others (CH3, O). As far as the negative ions are concerned, a number of species can be ionized in the reaction zone by three-body electron attachment and subsequent charge transfer processes (O2 initially, and then O, OH, HO2, HCOO and possibly HCOOO). Some of these negative ions are sufficiently strong bases to abstract protons from other species in proton transfer reactions (CH3OH, possibly H2O2, HCOOH, and perhaps the peroxidic intermediates HCOOO and HCOOOH). The remaining negative ions detected can be interpreted as cluster ions (OH− · H2O, HO2− · O2 or HO2− · CH3OH, CHO3− · H2O). All of this ion chemistry was compared with that observed previously for an analogous fuel-lean methane—oxygen flame. Many similarities were noted, particularly downstream, for both positive and negative ions. However, the combustion path leading to formic acid is more prominent in the methanol flame.

Mixing 2D electrons and atomic hydrogen on the liquid helium surface

Two-dimensional (2D) electrons on the liquid 4 He surface are mixed with atomic hydrogen. The density of 2D electrons decays as a result of the reaction with hydrogen atoms. The measured reaction rates indicates that two H atoms participate in the reaction to form a negative hydrogen ion, namely, H+H+e −→H −+H. Then, H − submerges into the liquid. A direct three-body process and dissociative attachment of electrons to excited H 2(14,4) molecules, which are produced by the surface recombination of hydrogen atoms, are discussed as a possible reaction mechanism.

Temperature and density effects on the properties of a long positive streamer in air

The 1.5D simulation is used to study the positive-streamer properties in air in a 20 cm sphere - plane gap versus gas temperature and density. It is shown that an increase in temperature up to 900 K at atmospheric pressure and a decrease in density by a factor of three at room temperature strongly affect the average electric field required for bridging the gap and the charge transferred through the streamer to the cathode; the temperature effect is much more pronounced than is the density effect. The calculated results qualitatively conform to available experimental data. The density effect is associated with a decrease in the rates of three-body processes such as three-body electron attachment to or conversion of ions into ions. The temperature effect is due to the decomposition of positive cluster ions which decreases the rate of dissociative electron - ion recombination. Electron attachment and detachment processes become important only when the electron density greatly decreases (by a factor of ten and more).

Three-body electron attachment to O 2(a 1Δ g)

Three-body electron attachment to O 2(a 1Δ g) has been studied theoretically using the Bloch—Bradbury mechanism of the process. Calculation of the attachment rate constant against the electron characteristic energy and the vibrational number of the O 2(A 1Δ g) molecule has been carried out. It has been shown that the electron attachment rate is substantially lower to O 2(a 1Δ g than to the O 2 molecule in the ground state.

Electron thermalization and attachment in pulse-irradiated oxygen studied by time-resolved microwave conductivity

The microwave conductivity of oxygen gas following nanosecond pulsed irradiation has been studied for pressures from 5 to 50 torr. The conductivity is found to decrease by a factor of approx. 20 in the early stages ( tN < 2 x 10 11 s cm -3) following the pulse. This is attributed to a decrease in the electron collision frequency as the initial excess energy of the electrons becomes degraded. A further decrease found at longer times is due to the three-body attachment of electrons to O 2 with a rate constant of 2.4 x 10 -30 cm 6s -1. Above a pressure of approx. 30 torr significant attachment begins to occur while electrons are still superthermal. The time at which the microwave signal is within 10% of the value corresponding to thermal energies is given by τ th P ≈ 15 μs.torr.

Three-body electron attachment to a molecule

Mechanisms for three-body electron attachment to a molecule are examined. Methods for studying this process experimentally are described. The measurements of the characteristics of the process and their dependence on the parameters of the molecule and the energy of the electron are presented. It is shown that electron attachment to a molecule in a gas and a liquid are related. It is shown that three-body attachment is important in the low-temperature plasma of the upper atmosphere, high-pressure discharges, and gaseous dielectrics.

Trekhchastichnoe prilipanie elektrona k molekule

Trekhchastichnoe prilipanie elektrona k molekule

Influence of water and ethanol vapors on the operation of air proportional counters

Influence of water and ethanol vapors was examined on the operation of cylindrical air proportional counters. These vapors depositing on the anode wire of the counter emitted a large amount of positive ions into the counter volume by a high electric field at the anode. The positive ion emission, however, never generated spurious pulses to be detected. The decrease of counting efficiency for β-rays observed by the addition of these vapors to the air could be explained by the decrease of the effective volume of the counter, which was generated by the promotion of three-body attachment of electrons to oxygen molecules. It was clarified that spurious pulses observed with the air containing these vapors were entirely due to the generation of leakage current through the surface of an insulator.

Hydrocarbon ions in fuel-rich, CH4–C2H2–O2 flames as a probe for the initiation of soot: interpretation of the ion chemistry

The ion chemistry is discussed for fuel-rich, nearly sooting, methane–oxygen flames at atmospheric pressure with added acetylene. Different types of ion–molecule reactions, both positive and negative, which can contribute through chemical ionization (CI) processes are summarized including their dependence on temperature, pressure, and equivalence ratio [Formula: see text]. Extensive data were presented previously involving ion concentration profiles measured with a mass spectrometer as a function of distance along the axis of conical flames. An understanding of the dominant CI processes provides insight into the early chemical stage of soot formation associated with the flame reaction zone. The negative ion profiles show moderately unsaturated hydrocarbon ions upstream formed by proton transfer followed by progressive dehydrogenation; the highly unsaturated, carbonaceous ions observed downstream appear to arise by two- and three-body electron attachment, charge transfer, and H-atom stripping. The negative hydrocarbon ions can all be explained in terms of polyacetylene derivatives. The same build-up of carbonaceous species downstream is evident from the positive ion profiles. A major role is ascribed to proton transfer reactions with lesser contributions from charge transfer and ion–molecule condensation; three-body association is probably insignificant. Experiments with added acetylene indicate extensive fuel pyrolysis early in the reaction zone. There is no evidence that an ionic mechanism is dominant in forming soot precursors compared with neutral condensation reactions. Because of complexities in the positive ion chemistry, the negative ions appear to provide the more straightforward probe of the underlying neutral chemistry.

Two- and three-body electron attachment in air

The rate of disappearance of electrons has been measured in mixtures of 20% O2 in N2. The results show a three-body attachment rate coefficient of 2*10-32 cm6 s-1 for electron mean energies in the range from 0.6 to 1.8 eV. The results also show a two-body rate coefficient which decreases from 8*10-13 to 5*10-14 cm3 s-1 over this same range.

Ionization in a methanol-oxygen flame

The combustion of methanol was studied in a conical methanol—oxygen flame of fuel-lean composition (equivalence ratio φ = 0.25) burning at atmospheric pressure surrounded by a flowing argon shield. Oxygen bubbled through liquid methanol contained in two gas saturators provided a premixed flame of excellent stability and reproducibility. The flame gas was sampled into a mass spectrometer which was used to detect a variety of naturally occurring ionic species, both positive and negative. Although the maximum level of ionization in this flame had the rather low value of 5 × 10 8 ions ml −1, nevertheless concentration profiles were drawn as a function of distance along the flame axis at 17 individual mass numbers ( m/z) for positive ions and 11 for negative ions; that is, whenever an appreciable signal could be detected below 100 amu. The positive profiles in the reaction zone are dominated by proton transfer processes which indicate that CHO + is the primary ion. A variety of protonated combustion intermediates and products were detected including both stable molecules (H 2O, HCHO, the CH 3OH fuel, CH 2CO, CH 3CHO, HCOOH and possibly CH 3OCH 3/C 2H 5OH) and radicals (C, CH, CH 2, HCO, CH 2OH or CH 3O, CH 3CO or CH 2CHO, and possibly CH 3OO). Chemical ionization by charge transfer is certainly operative for two species (O 2 and NO as an impurity) and perhaps others (CH 3, O). As far as the negative ions are concerned, a number of species can be ionized in the reaction zone by three-body electron attachment and subsequent charge transfer processes (O 2 initially, and then O, OH, HO 2, HCOO and possibly HCOOO). Some of these negative ions are sufficiently strong bases to abstract protons from other species in proton transfer reactions (CH 3OH, possibly H 2O 2, HCOOH, and perhaps the peroxidic intermediates HCOOO and HCOOOH). The remaining negative ions detected can be interpreted as cluster ions (OH − · H 2O, HO 2 − · O 2 or HO 2 − · CH 3OH, CHO 3 − · H 2O). All of this ion chemistry was compared with that observed previously for an analogous fuel-lean methane—oxygen flame. Many similarities were noted, particularly downstream, for both positive and negative ions. However, the combustion path leading to formic acid is more prominent in the methanol flame.