High Energy Electron Impact Research Articles

High-energy electron impact study on autoionizing region in helium by detection of ejected electrons

Ejected electron spectra from autoionizing region of He in the energy region of N=2 and N=3 Rydberg series have been measured at electron impact energies of 505, 1816 and 2018eV and ejection angles of 40°, 90° and 130°. At high electron impact energies and large ejection angles this energy region is dominated by optically allowed transitions, while optically forbidden transitions are less pronounced. At the angle of 40° optically forbidden states almost vanish and resonances dominate the spectrum. A new resonance at 64.18eV has been found at the angle of 40° and the electron impact energy of 505eV. In energy region above 65eV of excitation energy the first three levels of N=3 and the first level of N=4, Rydberg series have been measured. A good agreement in energy positions between these features and the corresponding ones reported by Domke et al.[2] was found.

A Generalized Sturmian Treatment of (e, 3e) Processes Described as a Three-Body Coulomb Problem

Fil: Ambrosio, Marcelo Jose. Universidad Nacional del Sur. Departamento de Fisica; Argentina

Effect of transmission losses on measured parameters in multi-ion coincidence momentum spectrometers

We address the effect of transmission losses on the measured kinematic parameters of molecular fragmentation processes in a time-of-flight based ion momentum spectrometer. We suggest means to correct for these losses for two-body fragmentation having isotropic distribution. As an example, we discuss the kinetic energy release spectrum observed in recoil ion momentum spectrometer of doubly ionized nitrogen molecules formed upon high energy electron impact. Further, we highlight the difficulties in calculating losses in many-body fragmentation and anisotropic emissions and show that such effects cannot be accounted without employing additional information about the process. In many cases, such information cannot be extracted from the observed data in the experiment and thus we have to rely on careful assumptions.

Determination of the electronic structure of atoms and molecules in the ground state: Measurement of molecular hydrogen by high-resolution x-ray scattering

The high-resolution x-ray-scattering technique is used to study the elastic scattering of atoms and molecules in the gas phase. The elastic squared form factor, which is the square of the Fourier transformation of the electron density distribution in position space and reveals the pure electronic structure of atoms and molecules in the ground state, of molecular hydrogen is measured at an incident photon energy of about 9889 eV and an energy resolution of about 70 meV. Although it is generally thought that the x-ray-scattering technique is identical to high-energy electron scattering, at least for elastic scattering these two techniques have an apparent difference, i.e., the pure electronic structure of a molecule in the ground state can be determined by x-ray scattering while it cannot be obtained by the high-energy electron impact method due to the interference between the scattering of separate nuclei and of the electrons in the target. The present experimental results match the theoretical calculations very well, which demonstrates that high-resolution x-ray scattering is a powerful tool to study the electronic structure of atoms and molecules in the ground state.

Charge symmetric dissociation of doubly ionized N2 and CO molecules.

We report a comparative study of the features in dissociative double ionization by high energy electron impact of N2 and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications. To understand these differences, potential energy curves (PECs) of dications have been computed using multi-reference configuration interaction method. The Franck-Condon factors and tunneling life times of vibrational levels of dications have also been computed. While the KER spectrum of N2 (++) can be readily explained by considering dissociation via repulsive states and tunneling of meta-stable states, indirect dissociation processes such as predissociation and autoionization have to be taken into account to understand the major features of the KER spectrum of CO(++). Direct and indirect processes identified on the basis of the PECs and experimental KER spectra also provide insights into the differences in the CSD-to-ND ratios.

Experimental Dose Enhancement in Multi-Layer Shielding Structures Exposed to High-Energy Electron Environments

The impact of high energy electrons in multi-layered shielding structures has been measured in terms of dose enhancement effects. New dosimetric data from a series of extensive experimental tests have been obtained and compared to the latest electromagnetic physics models included in the Geant4 Monte Carlo toolkit.

S-model calculations for high-energy-electron-impact double ionization of helium

In this paper the double ionization of helium by high-energy electron impact is studied. The corresponding four-body Schr\"odinger equation is transformed into a set of driven equations containing successive orders in the projectile-target interaction. The transition amplitude obtained from the asymptotic limit of the first-order solution is shown to be equivalent to the familiar first Born approximation. The first-order driven equation is solved within a generalized Sturmian approach for an $S$-wave $(e,3e)$ model process with high incident energy and small momentum transfer corresponding to published measurements. Two independent numerical implementations, one using spherical and the other hyperspherical coordinates, yield mutual agreement. From our ab initio solution, the transition amplitude is extracted, and single differential cross sections are calculated and could be taken as benchmark values to test other numerical methods in a previously unexplored energy domain.

Electron correlations in cross sections for ionization of heliumlike ions by high-energy particle impact

We have evaluated the dominant contribution of the electron correlations to the single $K$-shell ionization cross section of heliumlike atomic systems by impact of high-energy electrons. This study is performed consistently within the framework of nonrelativistic perturbation theory. The results obtained are also applicable for the case of high-energy collisions with arbitrary charged particles whose mass is much less than that of the target. The formula for cross section is represented in the form of a universal scaling. A comparison of our numerical calculations with available experimental data is made.

Desorption from Methanol and Ethanol Ices by High Energy Electrons: Relevance to Astrochemical Models

Methanol and ethanol, precursors of prebiotic molecules, are found in interstellar and circumstellar environments. At low temperatures, electrons may interact with these frozen molecules on dust grain surfaces stimulating desorption of atomic and molecular ions and charged clusters. These heavy fragments released from the icy mantles could contribute to the abundance in the gas phase of organic molecules in such environments. In this work, we investigate the ionic fragments desorbed from methanol and ethanol pure ices due to high energy electron impact. Absolute desorption yields (ions/impact) for each fragment desorbed from the ice surface were determined. Several clusters and heavier molecular ions were observed at higher electron energies. Two mechanisms seem to be involved in the desorption process, namely, the Auger stimulated ion desorption and that of secondary electrons. These data may provide support to establish more accurate astrochemical models and contribute to explain the influence of solar wind on condensed alcohols.

Effects of fibre-form nanostructures on particle emissions from a tungsten surface in plasmas

The effects of fibre-form nanostructure of a tungsten surface on both electron emission and sputtering in helium/argon plasmas are represented. Generally, a nano-fibre forest, the so-called ‘fuzz’, made of tungsten with helium gas inside is found to have the tendency of suppressing the particle emission substantially. The electron emission comes from the impact of high-energy primary electrons. In addition, a deeply biased tungsten target, which inhibits the influx of even energetic primary electrons, seems to produce an electron emission, and it may be suppressed on the way to nanostructure formation on the surface of the W target. Such an emission process is discussed here. The sputtering yield of the He-damaged tungsten surface with the fibre-form nanostructure depends on the surface morphology while the sputtering itself changes the surface morphology, so that the time evolutions of sputtering yield from the W surface with an originally well-developed nanostructure are found to show a minimum in sputtering yield, which is about a half for the fresh nanostructured tungsten and roughly one-fifth of the yield for the original flat normal tungsten surface. The surface morphology at that time is, for the first time, made clear with field emission scanning electron microscopy observation. The physical mechanism for the appearance of such a minimum in sputtering yield is discussed.

Pyrite-enhanced methylene blue degradation in non-thermal plasma water treatment reactor

In this study, methylene blue (MB) removal from an aqueous phase by electrical discharge non-thermal plasma (NTP) over water was investigated using three different feed gases: N2, Ar, and O2. The results showed that the dye removal rate was not strongly dependent on the feed gas when the electrical current was kept the same for all gases. The hydrogen peroxide generation in the water varied according to the feed gas (N2<Ar<O2). Using O2 as the feed gas, pyrite was added to the reactor in acid medium resulting in an accentuated increase in the dye removal, which suggests that pyrite acts as a Fenton-like catalyst. The total organic carbon (TOC) content of the dye solution decreased slightly as the plasma treatment time increased, but in the presence of the pyrite catalyst the TOC removal increased substantially. The acute toxicity test using Artemia sp. microcrustaceans showed that the treated solution is not toxic when Ar, O2 or O2–pyrite is employed. Electrospray ionization mass spectrometry analysis (ESI-MS) of the treated samples indicated that the dye degradation occurs via high energy electron impact as well as successive hydroxylation in the benzene rings of the dye molecules.

S055034 高温・高圧下でのDBD空気プラズマ流の反応性流動特性

Plasma is a multi-functional flow with high energy density. In the nonequilibrium plasma flow, active species such as radicals, excited species and charged particles are effectively generated by high energy electron impact reactions. Oxygen radical and ozone in plasma-generated active species have strong oxidation potential and play an important role in chemical reactions. Recently researches on the application of nonequiriblium plasma flow to combustion enhancement in an internal combustion engine has been extensively conducted. However, most of the researches of nonequilibrium plasma flow were conducted under atmospheric pressure condition and fundamental characteristics of nonequilibrium plasma under high pressure condition as in the internal engines have not been clarified in detail. It is important to clarify the fundamental characteristics of nonequilibrium plasma flow under high temperature and high pressure conditions. Therefore, the purpose of this research is to provide the fundamental data such as radicals and ozone generation in nonequilibrium plasma flow under high temperature and high pressure conditions for the application to combustion enhancement in an internal combustion engine. Experimental analysis of air plasma flow by dielectric barrier discharge was conducted. Fundamental characteristics of discharge such as the oxygen radical and ozone productions by dielectric barrier discharge for various operating conditions were discussed in detail.

Generation of cold electrons in the downstream region of a microwave plasma source with near boundary resonances for production of negative ions

A microwave driven multicusp plasma based volume negative ion source equipped with a magnetic filter is developed. Instead of employing any electrodes or current carrying filaments, microwaves of frequency 2.45 GHz is used to generate plasma by resonance heating mechanisms namely the electron cyclotron resonance (ECR) and upper hybrid resonances (UHR), occurring near the boundary plasma layers. The principal process of negative ion production in hydrogen is dissociative attachment of low energy (0.5–1.0 eV) electrons to vibrationally excited neutral molecules generated from high energy (15–20 eV) electron impact. The source therefore necessitates two distinct spatial regions (a) production and (b) attachment chambers; which would contain electrons with optimum cross section for the aforementioned processes. A biased grid after the magnetic filter further helps to lower down the electron temperature to ≤1 eV which is favorable for the dissociative attachment process.

The UV photofragmentation spectroscopy of the metal dication complex [Mn(pyridine)4]2+

A theoretical and experimental study has been undertaken of the gas phase UV photoexcitation spectrum of the metal dication complex [Mn(pyridine)4]2+. The ions have been prepared using a combination of the pick-up technique and high energy electron impact, and then held in a cold ion trap where they were excited with tuneable UV radiation. Spectra have been recorded by monitoring fragment ion yields as a function of laser wavelength following the excitation of [Mn(pyridine)4]2+ at wavelengths between 225 and 348 nm. For the range 225–263 nm the summation of photofragment ion intensities resulted in a spectrum that contained considerable structure. Although it has been possible to give regions of the spectrum a qualitative assignment to either metal-based or ligand-based transitions, a detailed comparison with results from the application of adiabatic time-dependent density functional theory (TDDFT) to provide an accurate assignment of the electronic transitions involved is considered unsound. This failure to model the excited state spectrum of the open-shell complex [Mn(pyridine)4]2+ is attributed to the significant double- and higher-excitation character of the excited states, which cannot be modelled by the strict single-electron excitations available from adiabatic TDDFT.

The generalized oscillator strengths for Na: monopole, dipole and quadrupole transitions

The generalized oscillator strengths (GOSs) of Na from the ground state [2p63s]32S excited to [2p6(n + 1)s](n + 1)2S, [2p6np]n2P, [2p6nd]n2D(3 ⩽ n ⩽ ∞) and adjacent continuum states are systematically investigated by the R-matrix method within the first Born approximation. The calculated energy levels of Na+ and Na are in good agreement with the experimental values. The energy dependence of the GOS extrema for the monopole, dipole and quadrupole transitions is investigated. The GOS density surfaces of 2S, 2P and 2D channels are calculated and their accuracies are tested rigorously by the available experiments as well as by the comparisons between the calculations on the different bases and the sum rule. With the surfaces tested, the high-energy electron impact excitation cross sections of the infinite Rydberg states near the threshold can be readily obtained by interpolations. In addition, the GOSDs for the resonance transitions 2p63s → 2p53s2 and 2p63s → 2p53s3p are investigated.

Kinetic Analysis of the Catalyst and Nonthermal Plasma Hybrid Reaction for Methane Steam Reforming

Bioresources, such as landfill gas and agricultural residues, attract considerable attention because of growing concerns of global energy and environmental protection. However, the efficient usage of bioresource poses major challenges and generally necessitates appropriate pre-reforming processes. We propose a low-temperature (300−500 °C) upgrading method using an atmospheric pressure nonthermal discharge generated in a reforming catalyst bed reactor for profitable recovery of poor bioresources. Excited species produced by high-energy electron impact, which proceed independent of the temperature, accelerate methane steam reforming at lower temperatures than normal catalyst reactions with minimum energy required. The resultant hydrogen-enriched biogas is then available for use in conventional energy utility systems, such as internal combustion engines. This paper introduces fundamental characteristics of nonthermal discharge and the catalyst hybrid reactor. Furthermore, a detailed mechanistic study of syne...

High-energy electron-impact excitation process: The generalized oscillator strengths of helium

The high-energy electron impact excitation cross sections are directly proportional to the generalized oscillator strengths (GOSs) of the target (an atom or molecule). In the present work, the GOSs of helium from the ground state to $n\phantom{\rule{0.2em}{0ex}}^{1}S$, $n\phantom{\rule{0.2em}{0ex}}^{1}P$, $n\phantom{\rule{0.2em}{0ex}}^{1}D$ $(n\ensuremath{\rightarrow}\ensuremath{\infty})$ and adjacent continuum excited states are calculated by a modified $R$-matrix code within the first Born approximation. In order to treat the bound-bound and bound-continuum transitions in a unified manner, the GOS density (GOSD) is defined based on the quantum defect theory. The GOSD surfaces of $^{1}S$, $^{1}P$, and $^{1}D$ channels are calculated and tested stringently by the recent experiments. With the recommended GOSD surfaces with sufficient accuracy, the GOSDs (i.e., GOSs) from the ground state into all $n\phantom{\rule{0.2em}{0ex}}^{1}S$, $n\phantom{\rule{0.2em}{0ex}}^{1}P$, and $n\phantom{\rule{0.2em}{0ex}}^{1}D$ excited states of helium can be obtained by interpolation. Thus, the high-energy electron impact excitation cross sections of all these excited states can be readily obtained. In addition to the high-energy electron impact excitation cross sections, a scheme to calculate the cross sections in the entire incident energy range is discussed.

Trapping and recording the collision- and photo-induced fragmentation patterns of multiply charged metal complexes in the gas phase

A quadrupole ion trap has been interfaced with a pick-up cluster ion source and a quadrupole mass filter in order to combine the storage capabilities of the trap with the advantages of the pick-up technique for producing a wide variety of multiply charged metal–ligand complexes. Complexes produced using the pick-up technique are ionized by high energy electron impact before passing through a quadrupole mass filter. The mass-selected ions are transmitted by ion guide and injected into a quadrupole ion trap, where they are accumulated for up to 1000 ms and further isolated to remove any reaction/charge transfer fragments. Following collision-induced dissociation (CID) or photoexcitation, ions are ejected from the trap and mass analyzed. CID experiments show that certain dication complexes are very susceptible to the presence of background water in the trap, but that collisional activation can provide a mechanism for revealing stable metal/ligand combinations. The results from preliminary photoexcitation experiments in the form of infrared multi-photon dissociation (IRMPD) are discussed in terms of fragmentation patterns and processes induced by Coulomb explosion. The instrumentation and experimental parameters are presented here together with preliminary results on selected doubly charged complexes containing Cu 2+, Mg 2+ and Zn 2+. The apparatus is evaluated in terms of performance with regard to being able to provide sufficient ion signal to store and study the reactivity and spectroscopy of a wide range of multiply charged ions in the gas phase.

Gas-Phase Study of the Chemistry and Coordination of Lead(II) in the Presence of Oxygen-, Nitrogen-, Sulfur-, and Phosphorus-Donating Ligands

Using a pickup technique in association with high-energy electron impact ionization, complexes have been formed in the gas phase between Pb(2+) and a wide range of ligands. The coordinating atoms are oxygen, nitrogen, sulfur, and phosphorus, together with complexes consisting of benzene and argon in association with Pb(2+). Certain ligands are unable to stabilze the metal dication, the most obvious group being water and the lower alcohols, but CS(2) is also unable to form [Pb(CS(2))(N)](2+) complexes. Unlike many other metal dication complexes, those associated with lead appear to exhibit very little chemical reactivity following collisional activation. Such reactions are normally promoted via charge transfer and are initiated using the energy difference between M(2+) + e(-) --> M(+) and L --> L(+) + e(-), which is typically approximately 5 eV. In the case of Pb(2+), this energy difference usually leads to the appearance of L(+) and the loss of a significant fraction of the remaining ligands as neutral species. In many instances, Pb(+) appears as a charge-transfer product. The only group of ligands to consistently exhibit chemical reactivity are those containing sulfur, where a typical product might be PbS(+)(L)(M) or PbSCH(3)(+)(L)(M).

The EPQ Code System for Simulating the Thermal Response of Plasma-Facing Components to High-Energy Electron Impact

The generation of runaway electrons during a thermal plasma disruption is a concern for the safe and economical operation of a tokamak power system. Runaway electrons have high energy, 10 to 300 MeV, and may potentially cause extensive damage to plasma-facing components (PFCs) through large temperature increases, melting of metallic components, surface erosion, and possible burnout of coolant tubes. The EPQ code system was developed to simulate the thermal response of PFCs to a runaway electron impact. The EPQ code system consists of several parts: UNIX scripts that control the operation of an electron-photon Monte Carlo code to calculate the interaction of the runaway electrons with the plasma-facing materials; a finite difference code to calculate the thermal response, melting, and surface erosion of the materials; a code to process, scale, transform, and convert the electron Monte Carlo data to volumetric heating rates for use in the thermal code; and several minor and auxiliary codes for the manipulation and postprocessing of the data. The electron-photon Monte Carlo code used was Electron-Gamma-Shower (EGS), developed and maintained by the National Research Center of Canada. The Quick-Therm-Two-Dimensional-Nonlinear (QTTN) thermal code solves the two-dimensional cylindrical modified heat conduction equation using the Quickest third-order accurate and stable explicit finite difference method and is capable of tracking melting or surface erosion. The EPQ code system is validated using a series of analytical solutions and simulations of experiments. The verification of the QTTN thermal code with analytical solutions shows that the code with the Quickest method is better than 99.9% accurate. The benchmarking of the EPQ code system and QTTN versus experiments showed that QTTN’s erosion tracking method is accurate within 30% and that EPQ is able to predict the occurrence of melting within the proper time constraints. QTTN and EPQ are verified and validated as able to calculate the temperature distribution, phase change, and surface erosion successfully.