Special Issue "Accelerator-Based Atomic Physics: Fast Ion–Atom and Ion–Molecule Collisions"

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

Deadline for manuscript submissions: closed (16 February 2021).

Special Issue Editor

Dr. Emmanouil P. Benis
E-Mail Website
Guest Editor
Department of Physics, University of Ioannina, GR 45110 Ioannina, Greece
Interests: fast ion-atom collisions; high resolution electron spectroscopy; pre-excited ion beams; state-selective studies; electron transfer; electron elastic scattering; cusp electrons; multi-open-shell ion states; hollow states; metastable states; cascade effects; electron spectrographs

Special Issue Information

Dear Colleagues,

Energetic ion beams delivered by accelerators have been the workhorse of atomic physics for more than 60 years. Modern accelerators provide a variety of ion species and charge states as exotic as bare uranium and velocities reaching deep into the relativistic regime. The strong interactions occurring in such energetic ion-impact collisions have shaped our understanding about the physics of the structure of the atomic world, and the dynamics involved during the collisions. Today, energetic ion-impact collisions continue to play a vital role in shedding light on fundamental processes and properties of atomic and molecular systems, thus providing data and insight for other research areas such as fusion and laser-induced plasmas, astrophysics, and radiation physics.

For this Special Issue, we invite original contributions covering all aspects of fast ion–atom and ion–molecule collisions including excitation, ionization, charge transfer, dissociation, and fragmentation for energetic collision velocities reaching up to the relativistic regime. Topics may include new theoretical or computational approaches, new experimental techniques, electron and X-ray spectroscopy data, calculations and measurements of cross sections, collision dynamics, and the use of collisional data in other research areas. The goal is to provide an overview of the current research in the field, and of new insights, developments, applications, and open problems.

Assist. Prof. Emmanouil Benis
Guest Editor

Manuscript Submission Information

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Keywords

  • fundamental processes in ion–atom and ion–molecule collisions
  • few-body dynamics
  • fragmentation of molecules and clusters by ion impact
  • ion–biomolecule interactions
  • laser-assisted collisions
  • coherence, electron–electron correlation, and relativistic effects
  • new developments, techniques and instrumentation
  • applications of ion-impact collisions

Published Papers (11 papers)

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Research

Open AccessArticle
Angular Distribution of Characteristic Radiation Following the Excitation of He-Like Uranium in Relativistic Collisions
Atoms 2021, 9(2), 20; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9020020 - 25 Mar 2021
Viewed by 438
Abstract
In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic K [...] Read more.
In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic Kα radiation following the K → L excitation of He-like uranium. We pay special attention to the magnetic sub-level population of the excited 1s2lj states, which is directly related to the angular distribution of the characteristic Kα radiation. We show that the experimental data can be well described by calculations taking into account the excitation by the target nucleus as well as by the target electrons. Moreover, we demonstrate for the first time an important influence of the electron-impact excitation process on the angular distributions of the Kα radiation produced by excitation of He-like uranium in collisions with different targets. Full article
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Open AccessArticle
Fundamental Parameters Related to Selenium Kα and Kβ Emission X-ray Spectra
Atoms 2021, 9(1), 8; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9010008 - 22 Jan 2021
Viewed by 631
Abstract
We present relativistic ab initio calculations of fundamental parameters for atomic selenium, based on the Multiconfiguration Dirac-Fock method. In detail, fluorescence yields and subshell linewidths, both of K shell, as well as Kβ to Kα intensity ratio are provided, showing overall [...] Read more.
We present relativistic ab initio calculations of fundamental parameters for atomic selenium, based on the Multiconfiguration Dirac-Fock method. In detail, fluorescence yields and subshell linewidths, both of K shell, as well as Kβ to Kα intensity ratio are provided, showing overall agreement with previous theoretical calculations and experimental values. Relative intensities were evaluated assuming the same ionization cross-section for the K-shell hole states, leading to a statistical distribution of these initial states. A method for estimating theoretical linewidths of X-ray lines, where the lines are composed by a multiplet of fine-structure levels that are spread in energy, is proposed. This method provides results that are closer to Kα1,2 experimental width values than the usual method, although slightly higher discrepancies occur for the Kβ1,3 lines. This indicates some inaccuracies in the calculation of Auger rates that have a higher contribution for partial linewidths of the subshells involved in the Kβ1,3 profile. Apart from this, the calculated value of Kβ to Kα intensity ratio, which is less sensitive to Auger rates issues, is in excellent agreement with recommended values. Full article
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Open AccessArticle
A Complete CDW Theory for the Single Ionization of Multielectronic Atoms by Bare Ion Impact
Atoms 2021, 9(1), 3; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9010003 - 13 Jan 2021
Viewed by 465
Abstract
A complete form of the post version of the continuum distorted wave (CDW) theory is used to investigate the single ionization of multielectronic atoms by fast bare heavy ion beams. The influence of the non-ionized electrons on the dynamic evolution is included through [...] Read more.
A complete form of the post version of the continuum distorted wave (CDW) theory is used to investigate the single ionization of multielectronic atoms by fast bare heavy ion beams. The influence of the non-ionized electrons on the dynamic evolution is included through a residual target potential considered as a non-Coulomb central potential through a GSZ parametric one. Divergences found in the transition amplitude containing the short-range part of the target potential are avoided by considering, in that term exclusively, an eikonal phase instead of the continuum factor as the initial channel distortion function. In this way, we achieve the inclusion of the interaction between the target active electron and the residual target, giving place to a more complete theory. The present analysis is supported by comparisons with existing experimental electron emission spectra and other distorted wave theories. Full article
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Open AccessArticle
Calculations of Electron Loss to Continuum in Collisions of Li- and Be-Like Uranium Ions with Nitrogen Targets
Atoms 2020, 8(4), 89; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8040089 - 04 Dec 2020
Viewed by 650
Abstract
Doubly differential cross sections for projectile ionization in fast collisions of few-electron uranium ions with the nitrogen target are calculated within the first order of the relativistic perturbation theory. A comparison with the recent measurements of the energy distribution of forward-emitted electrons is [...] Read more.
Doubly differential cross sections for projectile ionization in fast collisions of few-electron uranium ions with the nitrogen target are calculated within the first order of the relativistic perturbation theory. A comparison with the recent measurements of the energy distribution of forward-emitted electrons is made and good agreement is found. Full article
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Open AccessArticle
Radiative Cascade Repopulation of 1s2s2p 4P States Formed by Single Electron Capture in 2–18 MeV Collisions of C4+ (1s2s 3S) with He
Atoms 2020, 8(3), 61; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8030061 - 21 Sep 2020
Viewed by 589
Abstract
This study focuses on the details of cascade repopulation of doubly excited triply open-shell C3+(1s2s2p)4P and 2P± states produced in 2–18 MeV collisions of C4+(1 [...] Read more.
This study focuses on the details of cascade repopulation of doubly excited triply open-shell C3+(1s2s2p)4P and 2P± states produced in 2–18 MeV collisions of C4+(1s2s3S) with He. Such cascade calculations are necessary for the correct determination of the ratio R of their cross sections, used as a measure of spin statistics [Madesis et al. PRL 124 (2020) 113401]. Here, we present the details of our cascade calculations within a new matrix formulation based on the well-known diagrammatic cascade approach [Curtis, Am. J. Phys. 36 (1968) 1123], extended to also include Auger depopulation. The initial populations of the 1s2sn4L and 1s2sn2L levels included in our analysis are obtained from the direct n single electron capture (SEC) cross sections, calculated using the novel three-electron close-coupling (3eAOCC) approach. All relevant radiative branching ratios (RBR) for n4 were computed using the COWAN code. While doublet RBRs are found to be very small, quartet RBRs are found to be large, indicating cascade feeding to be important only for quartets, consistent with previous findings. Calculations including up to third order cascades, extended to n using an n3 SEC model, showed a ∼60% increase of the 1s2s2p4P populations due to cascades, resulting, for the first time, in R values in good overall agreement with experiment. Full article
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Open AccessArticle
Net Electron Capture in Collisions of Multiply Charged Projectiles with Biologically Relevant Molecules
Atoms 2020, 8(3), 59; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8030059 - 17 Sep 2020
Viewed by 769
Abstract
A model for the description of proton collisions from molecules composed of atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus (H, C, N, O, P) was recently extended to treat collisions with multiply charged ions with a focus on net ionization. Here [...] Read more.
A model for the description of proton collisions from molecules composed of atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus (H, C, N, O, P) was recently extended to treat collisions with multiply charged ions with a focus on net ionization. Here we complement the work by focusing on net capture. The ion–atom collisions are computed using the two-center basis generator method. The atomic net capture cross sections are then used to assemble two models for ion–molecule collisions: An independent atom model (IAM) based on the Bragg additivity rule (labeled IAM-AR), and also the so-called pixel-counting method (IAM-PCM) which introduces dependence on the orientation of the molecule during impact. The IAM-PCM leads to significantly reduced capture cross sections relative to IAM-AR at low energies, since it takes into account the overlap of effective atomic cross sectional areas. We compare our results with available experimental and other theoretical data focusing on water vapor (H2O), methane (CH4) and uracil (C4H4N2O2). For the water molecule target we also provide results from a classical-trajectory Monte Carlo approach that includes dynamical screening effects on projectile and target. For small molecules dominated by a many-electron atom, such as carbon in methane or oxygen in water, we find a saturation phenomenon for higher projectile charges (q=3) and low energies, where the net capture cross section for the molecule is dominated by the net cross section for the many-electron atom, and the net capture cross section is not proportional to the total number of valence electrons. Full article
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Open AccessArticle
Simulations of Ion-Guiding Through Insulating Nanocapillaries of Varying Diameter: Interpretation of Experimental Results
Atoms 2020, 8(3), 48; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8030048 - 21 Aug 2020
Cited by 1 | Viewed by 643
Abstract
The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne7+ ions injected into capillaries with diameters ranging from 100 [...] Read more.
The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne7+ ions injected into capillaries with diameters ranging from 100 nm to 400 nm. In the calculations, non-linear effects are applied to model the charge transport along the capillary surface and into the bulk depleting the deposited charges from the capillary walls. In addition to the surface carrier mobility, the non-linear effects are also implemented into the bulk conductivity. A method is presented to determine the parameters of the surface charge transport and the bulk conductivity by reproducing the oscillatory structure of the mean emission angle. A common set of charge depletion rates are determined with relatively high accuracy providing confidence in the present theoretical analysis. Significant differences in the oscillatory structures, experimentally observed, are explained by the calculations. Experimental and theoretical results of the guiding power for capillaries of different diameters are compared. Finally, dynamic non-linear effects on the surface and bulk relaxation rates are determined from the simulations. Full article
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Open AccessArticle
Ionization Cross Sections in the Collision between Two Ground State Hydrogen Atoms at Low Energies
Atoms 2020, 8(2), 31; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8020031 - 22 Jun 2020
Viewed by 795
Abstract
The interaction between two ground state hydrogen atoms in a collision was studied using the four-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for the single ionization of the target, the ionization of the [...] Read more.
The interaction between two ground state hydrogen atoms in a collision was studied using the four-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for the single ionization of the target, the ionization of the projectile, resulting from pure ionization, and also from the electron transfer (capture or loss) processes. We also present cross sections for the complete break of the system, resulting in the final channel for four free particles. The calculations were carried out at low energies, relevant to the interest of fusion research. We present our cross sections in the projectile energy range between 2.0 keV and 100 keV and compare them with previously obtained theoretical and experimental results. Full article
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Open AccessArticle
Interaction of Be4+ and Ground State Hydrogen Atom—Classical Treatment of the Collision
Atoms 2020, 8(2), 27; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8020027 - 03 Jun 2020
Viewed by 962
Abstract
The interaction between Be4+ and hydrogen atom is studied using the three-body classical trajectory Monte Carlo method (CTMC) and the quasiclassical trajectory Monte Carlo method of Kirschbaum and Wilets (QTMC-KW). We present total cross sections for target ionization, target excitation, and charge [...] Read more.
The interaction between Be4+ and hydrogen atom is studied using the three-body classical trajectory Monte Carlo method (CTMC) and the quasiclassical trajectory Monte Carlo method of Kirschbaum and Wilets (QTMC-KW). We present total cross sections for target ionization, target excitation, and charge exchange to the projectile bound states. Calculations are carried out in the projectile energy range between 10 and 1000 keV/au, relevant to the interest of fusion research when the target hydrogen atom is in the ground state. Our results are compared with previous theoretical results. We found that the classical treatment describes reasonably well the cross sections for various final channels. Moreover, we show that the calculations by the QTMC-KW model significantly improve the obtained cross sections. Full article
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Open AccessArticle
Doubly and Triply Differential Cross Sections for Single Ionization of He by Fast Au53+ Using a Multi-Body Quasiclassical Model
Atoms 2020, 8(2), 19; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8020019 - 06 May 2020
Viewed by 753
Abstract
A multi-body multi-center quasiclassical model was used to determine doubly- and triply-differential cross sections following single ionization in 3.6 MeV/amu Au53+ + He collisions. The present model improved recent calculations, in which free electrons were added in the collision to reproduce, at [...] Read more.
A multi-body multi-center quasiclassical model was used to determine doubly- and triply-differential cross sections following single ionization in 3.6 MeV/amu Au53+ + He collisions. The present model improved recent calculations, in which free electrons were added in the collision to reproduce, at least qualitatively, the experimental binary peak. In the present calculations, the electrons, that were assumed to originate from the collisions of Au53+ with surfaces before colliding with the He target, were now considered to be in the field of the projectile, with nearly the same velocity. The agreement between the calculations and the experiment was improved, for both the doubly- and the triply-differential cross sections and was better than previous calculations based on quantum mechanics. Full article
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Open AccessEditor’s ChoiceArticle
Differential Study of Projectile Coherence Effects on Double Capture Processes in p + Ar Collisions
Atoms 2020, 8(2), 10; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms8020010 - 28 Mar 2020
Viewed by 1239
Abstract
We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were [...] Read more.
We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were found for double capture, but not for double capture plus ionization. The results suggest that multiple projectile–target interactions can lead to a significant weakening of projectile coherence effects. Full article
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