Special Issue "Electron Scattering in Gases –from Cross Sections to Plasma Modeling"

A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: 15 November 2021.

Special Issue Editor

Prof. Dr. Grzegorz Piotr Karwasz
E-Mail Website
Guest Editor
Institute of Physics, Uniwersytet Mikołaja Kopernika w Toruniu, 87 100 Torun, Poland
Interests: atomic physics; spectroscopy; electron and positron scattering; solid state physics; didactics of sciences

Special Issue Information

Dear Colleagues,

The first experiments on electron scattering were completed before the “official” discovery of this particle by J. J. Thomson. In spite of this, our knowledge of cross sections is still far from complete.

More recent experiments had some unexpected results, like selective fragmentation of DNA constituents by low-energy electrons, or “reverse” phenomena, i.e., synthesis of simple amino acids from inorganic precursors, triggered by slow electrons. The most recent need for cross sections comes from modeling plasmas for industrial and thermonuclear applications, and atmospheres of solar and extra-solar planets.

Both fundamental research (experiments, theory, reviews) and applications of electron-scattering cross sections in various processes are welcome.

Prof. Grzegorz Piotr Karwasz
Guest Editor

Manuscript Submission Information

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Published Papers (11 papers)

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Research

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Article
Targeted Cross-Section Calculations for Plasma Simulations
Atoms 2021, 9(4), 85; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9040085 - 21 Oct 2021
Viewed by 160
Abstract
Gathering data on electron collisions in plasmas is a vital part of conducting plasma simulations. However, data on neutral radicals and neutrals formed in the plasma by reactions between different radicals are usually not readily available. While these cross-sections can be calculated numerically, [...] Read more.
Gathering data on electron collisions in plasmas is a vital part of conducting plasma simulations. However, data on neutral radicals and neutrals formed in the plasma by reactions between different radicals are usually not readily available. While these cross-sections can be calculated numerically, this is a time-consuming process and it is not clear from the outset which additional cross-sections are needed for a given plasma process. Hence, identifying species for which additional cross-sections are needed in advance is highly advantageous. Here, we present a structured approach to do this. In this, a chemistry set using estimated data for unknown electron collisions is run in a global plasma model. The results are used to rank the species with regard to their influence on densities of important species such as electrons or neutrals inducing desired surface processes. For this, an algorithm based on graph theory is used. The species ranking helps to make an informed decision on which cross-sections need to be calculated to improve the chemistry set and which can be neglected to save time. The validity of this approach is demonstrated through an example in an SF6/O2 plasma. Full article
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Article
Electron Impact Excitation of Extreme Ultra-Violet Transitions in Xe7+ – Xe10+ Ions
Atoms 2021, 9(4), 76; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9040076 - 06 Oct 2021
Viewed by 312
Abstract
In the present work, a detailed study on the electron impact excitation of Xe7+, Xe8+, Xe9+ and Xe10+ ions for the dipole allowed (E1) transitions in the EUV range of 8–19 nm is [...] Read more.
In the present work, a detailed study on the electron impact excitation of Xe7+, Xe8+, Xe9+ and Xe10+ ions for the dipole allowed (E1) transitions in the EUV range of 8–19 nm is presented. The multi-configuration Dirac–Fock method is used for the atomic structure calculation including the Breit and QED corrections along with the relativistic configuration interaction approach. We have compared our calculated energy levels, wavelengths and transition rates with other reported experimental and theoretical results. Further, the relativistic distorted wave method is used to calculate the cross sections from the excitation threshold to 3000 eV electron energy. For plasma physics applications, we have reported the fitting parameters of these cross sections using two different formulae for low and high energy ranges. The rate coefficients are also obtained using our calculated cross sections and considering the Maxwellian electron energy distribution function in the electron temperature range from 5 eV to 100 eV. Full article
Article
Electron Ionization of Size-Selected Positively and Negatively Charged Helium Droplets
Atoms 2021, 9(4), 74; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9040074 - 05 Oct 2021
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Abstract
A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam [...] Read more.
A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role. Full article
Article
Magnetic Angle Changer for Studies of Electronically Excited Long-Living Atomic States
Atoms 2021, 9(4), 71; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9040071 - 28 Sep 2021
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Abstract
A new geometry of a magnetic angle changer (MAC) device is proposed, which allows experiments to be run on electron impact excitation of long-lived states of target atoms. The details of the device’s design are presented and discussed together with a numerical analysis [...] Read more.
A new geometry of a magnetic angle changer (MAC) device is proposed, which allows experiments to be run on electron impact excitation of long-lived states of target atoms. The details of the device’s design are presented and discussed together with a numerical analysis of its magnetic field. Full article
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Article
Vibrational Excitation Cross-Section by Positron Impact: A Wave-Packet Dynamics Study
Atoms 2021, 9(3), 64; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030064 - 09 Sep 2021
Viewed by 373
Abstract
The vibrational excitation cross-section of a diatomic molecule by positron impact is obtained using wave-packet propagation techniques. The dynamics study was carried on a two-dimensional potential energy surface, which couples a hydrogenlike harmonic oscillator to a positron via a spherically symmetric correlation polarization [...] Read more.
The vibrational excitation cross-section of a diatomic molecule by positron impact is obtained using wave-packet propagation techniques. The dynamics study was carried on a two-dimensional potential energy surface, which couples a hydrogenlike harmonic oscillator to a positron via a spherically symmetric correlation polarization potential. The cross-section for the excitation of the first vibrational mode is in good agreement with previous reports. Our model suggests that a positron couples to the target vibration by responding instantly to an interaction potential, which depends on the target vibrational coordinate. Full article
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Article
Cross Sections and Rate Coefficients for Vibrational Excitation of H2O by Electron Impact
Atoms 2021, 9(3), 62; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030062 - 06 Sep 2021
Viewed by 566
Abstract
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for [...] Read more.
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments. Full article
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Article
Relativistic Study on the Scattering of e± from Atoms and Ions of the Rn Isonuclear Series
Atoms 2021, 9(3), 59; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030059 - 27 Aug 2021
Viewed by 440
Abstract
Calculations are presented for differential, integrated elastic, momentum transfer, viscosity, inelastic, total cross sections and spin polarization parameters S, T and U for electrons and positrons scattering from atoms and ions of radon isonuclear series in the energy range from 1 eV–1 MeV. [...] Read more.
Calculations are presented for differential, integrated elastic, momentum transfer, viscosity, inelastic, total cross sections and spin polarization parameters S, T and U for electrons and positrons scattering from atoms and ions of radon isonuclear series in the energy range from 1 eV–1 MeV. In addition, we analyze systematically the details of the critical minima in the elastic differential cross sections along with the positions of the corresponding maximum polarization points in the Sherman function for the aforesaid scattering systems. Coulomb glory is investigated across the ionic series. A short range complex optical potential, comprising static, polarization and exchange (for electron projectile) potentials, is used to describe the scattering from neutral atom. This potential is supplemented by the Coulomb potential for the same purpose for a charged atom. The Dirac partial wave analysis, employing the aforesaid potential, is carried out to calculate the aforesaid scattering observables. A comparison of our results with other theoretical findings shows a reasonable agreement over the studied energy range. Full article
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Article
Accurate Electron Drift Mobility Measurements in Moderately Dense Helium Gas at Several Temperatures
Atoms 2021, 9(3), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030052 - 04 Aug 2021
Cited by 1 | Viewed by 473
Abstract
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. [...] Read more.
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities. Full article
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Article
On the Electron Impact Integral Cross-Sections for Butanol and Pentanol Isomers
Atoms 2021, 9(3), 43; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030043 - 13 Jul 2021
Viewed by 649
Abstract
The need for a reliable and comprehensive database of cross-sections for many atomic and molecular species is immense due to its key role in R&D domains such as plasma modelling, bio-chemical processes, medicine and many other natural and technological environments. Elastic, momentum transfer [...] Read more.
The need for a reliable and comprehensive database of cross-sections for many atomic and molecular species is immense due to its key role in R&D domains such as plasma modelling, bio-chemical processes, medicine and many other natural and technological environments. Elastic, momentum transfer and total cross-sections of butanol and pentanol isomers by the impact of 6–5000 eV electrons are presented in this work. The calculations were performed by employing the spherical complex optical potential formalism along with single-centre expansion and group additivity rule. The investigations into the presence of isomeric variations reveal that they are more pronounced at low and intermediate energies. Elastic, total cross-sections (with the exception of n-pentanol) and momentum transfer cross-sections for all pentanol isomers are reported here for the first time, to the best of our knowledge. Our momentum transfer cross-sections for butanol isomers are in very good agreement with the experimental and theoretical values available, and in reasonable consensus for other cross-sections. Full article
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Article
Few Body Effects in the Electron and Positron Impact Ionization of Atoms
Atoms 2021, 9(2), 33; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9020033 - 09 Jun 2021
Viewed by 888
Abstract
Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both [...] Read more.
Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both positrons and electrons as projectiles has opened up the possibility of performing complementary studies which could effectively isolate competing interactions that cannot be separately detected in an experiment with a single projectile. Results will be presented in kinematics where the electron impact ionization appears to be well understood and using the same kinematics positron cross sections will be presented. The kinematics are then varied in order to focus on the role of distortion, post collision interaction (pci), and interference effects. Full article
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Review

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Review
A Missing Puzzle in Dissociative Electron Attachment to Biomolecules: The Detection of Radicals
Atoms 2021, 9(4), 77; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9040077 - 07 Oct 2021
Viewed by 373
Abstract
Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide [...] Read more.
Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide have probed these processes in the past, and many significant achievements have been made, some technical challenges have hindered researchers from obtaining a complete picture of DEA. Therefore, this research perspective calls urgently for the implementation of advanced techniques to identify non-charged radicals that form from such a decomposition of gas-phase molecules. Having well-described DEA products offers a promise to benefit society by straddling the boundary between physics, chemistry, and biology, and it brings the tools of atomic and molecular physics to bear on relevant issues of radiation research and medicine. Full article
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