Research

Jump to: Review

10 pages, 3117 KiB

Open AccessCommunication

Interaction of Electrons and Positrons with Protons Aligned in One-Dimension Line

by Musab S. Al-Ajaleen and Károly Tőkési

Atoms 2023, 11(3), 46; https://doi.org/10.3390/atoms11030046 - 03 Mar 2023

Cited by 1 | Viewed by 1068

We present theoretical studies of electron and positron interaction with protons aligned in a one-dimension periodic line. The equally spaced protons were artificially generated where the individual protons are fixed in a certain position. The incident energies were 500 eV and 1000 eV. [...] Read more.

We present theoretical studies of electron and positron interaction with protons aligned in a one-dimension periodic line. The equally spaced protons were artificially generated where the individual protons are fixed in a certain position. The incident energies were 500 eV and 1000 eV. The electron and positron trajectories passing through these periodic multiple scattering objects were calculated using a classical trajectory Monte Carlo method. We show that this proton configuration has focusing and defocusing properties depending on the certain initial conditions. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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10 pages, 7057 KiB

Open AccessCommunication

Differential Description of Multiple Ionization of Uracil by 3.5 MeV/u C⁶⁺ Impact

by N. D. Cariatore, N. Bachi and S. Otranto

Atoms 2023, 11(2), 38; https://doi.org/10.3390/atoms11020038 - 11 Feb 2023

Cited by 1 | Viewed by 942

Abstract

In this work, a theoretical analysis of the impact of the multiple ionization of uracil by 3.5 MeV/u C

^{6 +}

is developed in the framework of a classical trajectory Monte Carlo method, as recently introduced for multi-electronic targets. The electron emission contribution [...] Read more.

In this work, a theoretical analysis of the impact of the multiple ionization of uracil by 3.5 MeV/u C

^{6 +}

is developed in the framework of a classical trajectory Monte Carlo method, as recently introduced for multi-electronic targets. The electron emission contribution arising from the multiple electron ionization is explicitly determined and the emission geometries and the reaction regions for double and triple ionization are explicitly identified. The present results suggest that double ionization is mainly characterized by the emission of slow electrons with a relative angle of 80

^{\circ}

–120

^{\circ}

. For triple ionization, on the other hand, the emission seems to occur with the three electrons holding similar interelectronic angles. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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13 pages, 1761 KiB

Open AccessArticle

Proton and Electron Irradiations of CH₄:H₂O Mixed Ices

by Duncan V. Mifsud, Péter Herczku, Béla Sulik, Zoltán Juhász, István Vajda, István Rajta, Sergio Ioppolo, Nigel J. Mason, Giovanni Strazzulla and Zuzana Kaňuchová

Atoms 2023, 11(2), 19; https://doi.org/10.3390/atoms11020019 - 22 Jan 2023

Cited by 2 | Viewed by 2080

Abstract

The organic chemistry occurring in interstellar environments may lead to the production of complex molecules that are relevant to the emergence of life. Therefore, in order to understand the origins of life itself, it is necessary to probe the chemistry of carbon-bearing molecules [...] Read more.

The organic chemistry occurring in interstellar environments may lead to the production of complex molecules that are relevant to the emergence of life. Therefore, in order to understand the origins of life itself, it is necessary to probe the chemistry of carbon-bearing molecules under conditions that simulate interstellar space. Several of these regions, such as dense molecular cores, are exposed to ionizing radiation in the form of galactic cosmic rays, which may act as an important driver of molecular destruction and synthesis. In this paper, we report the results of a comparative and systematic study of the irradiation of CH₄:H₂O ice mixtures by 1 MeV protons and 2 keV electrons at 20 K. We demonstrate that our irradiations result in the formation of a number of new products, including both simple and complex daughter molecules such as C₂H₆, C₃H₈, C₂H₂, CH₃OH, CO, CO₂, and probably also H₂CO. A comparison of the different irradiation regimes has also revealed that proton irradiation resulted in a greater abundance of radiolytic daughter molecules compared to electron irradiation, despite a lower radiation dose having been administered. These results are important in the context of the radiation astrochemistry occurring within the molecular cores of dense interstellar clouds, as well as on outer Solar System objects. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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13 pages, 868 KiB

Open AccessArticle

Binary Encounter Electrons in Fast Dressed-Ion–H₂ Collisions: Distorted Wave Theories and Experiment

by Nicolás J. Esponda, Stefanos Nanos, Michele A. Quinto, Theo J. M. Zouros, Roberto D. Rivarola, Emmanouil P. Benis and Juan M. Monti

Atoms 2023, 11(2), 17; https://doi.org/10.3390/atoms11020017 - 20 Jan 2023

Cited by 1 | Viewed by 1174

Abstract

We report measurements of double differential cross section for zero-degree binary encounter electrons emitted in collisions of 4.9 MeV and 13 MeV B

^{(2 - 5) +}

ions with H₂ targets. The corresponding calculations based on continuum distorted-wave (CDW) theories [...] Read more.

We report measurements of double differential cross section for zero-degree binary encounter electrons emitted in collisions of 4.9 MeV and 13 MeV B

^{(2 - 5) +}

ions with H₂ targets. The corresponding calculations based on continuum distorted-wave (CDW) theories are critically compared to the measurements. CDW in its post form exhibits a very good agreement with the measurements in all cases. The CDW theories utilized along with the well-known eikonal-initial-state (CDW-EIS) approximation are also examined and their results are compared to both the measurements and the CDW calculations. In particular, CDW-EIS using a recently proposed dynamic effective charge for the final channel projectile distortion exhibits a substantial improvement in comparison with an effective net-charge approximation. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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10 pages, 3889 KiB

Open AccessArticle

Electron-Impact Ionization of Carbon

by Nicolás Bachi, Sebastian Otranto and Karoly Tőkési

Atoms 2023, 11(2), 16; https://doi.org/10.3390/atoms11020016 - 20 Jan 2023

Cited by 4 | Viewed by 1303

Abstract

We present ionization cross-sections of collisions between electrons and carbon atoms using the classical trajectory Monte Carlo method. Total cross-sections are benchmarked against the reported experimental data and the predictions of numerically intensive theoretical methods as well as pioneering calculations for this collision [...] Read more.

We present ionization cross-sections of collisions between electrons and carbon atoms using the classical trajectory Monte Carlo method. Total cross-sections are benchmarked against the reported experimental data and the predictions of numerically intensive theoretical methods as well as pioneering calculations for this collision system. At impact energies greater than about 100 eV, the present results are in very good agreement with the generalized oscillator strength formulation of the Born approximation as well as with the experimental data. Limitations inherent to a purely classical description of the electron impact ionization process at low impact energies are detected and analyzed, suggesting a clear route for future studies. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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12 pages, 599 KiB

Open AccessArticle

Differential Analysis of the Positron Impact Ionization of Hydrogen in Debye Plasmas

by Emiliano Acebal, Sergio Hernan Martínez and Sebastian Otranto

Atoms 2023, 11(2), 15; https://doi.org/10.3390/atoms11020015 - 18 Jan 2023

Cited by 1 | Viewed by 1231

Abstract

In this work, a theoretical differential analysis of the positron impact ionization of hydrogen embedded in weakly coupled plasmas at an impact energy of 80 eV is developed. While the total and singly differential cross sections are analyzed within the classical trajectory Monte [...] Read more.

In this work, a theoretical differential analysis of the positron impact ionization of hydrogen embedded in weakly coupled plasmas at an impact energy of 80 eV is developed. While the total and singly differential cross sections are analyzed within the classical trajectory Monte Carlo method, a Born-3DW model for screened environments, recently introduced by the authors, is used to provide a fully differential view of the process. The present results suggest that the electron emission spectra are strongly affected by the level of screening of the surrounding medium, mainly due to the loss of the postcollisional interaction mechanism. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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9 pages, 279 KiB

Open AccessArticle

L-Shell Ionization Cross Sections for Silver by Low-Energy Electron Impacts

by Takeshi Mukoyama and Károly Tőkési

Atoms 2022, 10(4), 116; https://doi.org/10.3390/atoms10040116 - 19 Oct 2022

Cited by 2 | Viewed by 1203

Abstract

The L-subshell ionization cross sections and total L–X-ray production cross sections for the Ag atom by the electron impact near the ionization threshold were calculated with a classical-trajectory Monte Carlo method. The results were compared with experimental data, quantum mechanical calculations, and the [...] Read more.

The L-subshell ionization cross sections and total L–X-ray production cross sections for the Ag atom by the electron impact near the ionization threshold were calculated with a classical-trajectory Monte Carlo method. The results were compared with experimental data, quantum mechanical calculations, and the cross sections by positron impact. It was demonstrated that the classical treatments are useful for electron–atom collisions at energies higher than about six times the binding energies of target electrons but overestimate L-shell ionization and L–X-ray production cross sections at low energies near the threshold. Possible reasons for this discrepancy are discussed. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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10 pages, 2204 KiB

Open AccessArticle

Surface and Bulk Plasmon Excitation on Aluminum Surface at Small to High Grazing Angles

by Attila Sulyok and Karoly Tőkési

Atoms 2022, 10(4), 104; https://doi.org/10.3390/atoms10040104 - 30 Sep 2022

Cited by 1 | Viewed by 1371

Abstract

We present a series of spectra measured by reflected electron energy loss spectroscopy on an aluminum sample using a cylindrical mirror analyzer. The measurements were performed in the energy range between 250 eV and 2000 eV and with various incident angles, including the [...] Read more.

We present a series of spectra measured by reflected electron energy loss spectroscopy on an aluminum sample using a cylindrical mirror analyzer. The measurements were performed in the energy range between 250 eV and 2000 eV and with various incident angles, including the grazing geometry of an 88° incident angle. The observed spectra were evaluated and decomposed for surface and bulk excitation. The determined surface plasmon excitations were compared to the elastic peak and to the bulk excitation. We found a slight surface plasmon energy shift with altering glancing angles. We show that this shift exists independently from the bulk plasmon interference. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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7 pages, 685 KiB

Open AccessArticle

nl-Selective Classical Charge-Exchange Cross Sections in Be⁴⁺ and Ground State Hydrogen Atom Collisions

by Iman Ziaeian and Károly Tőkési

Atoms 2022, 10(3), 90; https://doi.org/10.3390/atoms10030090 - 09 Sep 2022

Cited by 2 | Viewed by 1403

Abstract

Charge-exchange cross sections in Be⁴⁺ + H(1s) collisions are calculated using the three-body classical trajectory Monte Carlo method (CTMC) and the quasi-classical trajectory Monte Carlo method of Kirschbaum and Wilets (QCTMC) for impact energies between 10 keV/amu and 300 keV/amu. We present [...] Read more.

Charge-exchange cross sections in Be⁴⁺ + H(1s) collisions are calculated using the three-body classical trajectory Monte Carlo method (CTMC) and the quasi-classical trajectory Monte Carlo method of Kirschbaum and Wilets (QCTMC) for impact energies between 10 keV/amu and 300 keV/amu. We present charge-exchange cross sections in the projectile n = 2 and nl = 2s, 2p states. Our results are compared with the previous quantum-mechanical approaches. We found that the QCTMC model is a powerful classical model to describe the state-selective charge-exchange cross sections at lower impact energies and the QCTMC results are in good agreement with previous observations. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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13 pages, 894 KiB

Open AccessArticle

Photon Emission from Hollow Ions Near Surfaces

by Stephan Fritzsche

Atoms 2022, 10(2), 37; https://doi.org/10.3390/atoms10020037 - 10 Apr 2022

Cited by 1 | Viewed by 2091

Abstract

Ions with multiple inner-shell vacancies frequently arise due to their interaction with different targets, such as (intense) light pulses, atoms, clusters or bulk material. They are formed, in addition, if highly charged ions approach surfaces and capture electrons at rather large distances. To [...] Read more.

Ions with multiple inner-shell vacancies frequently arise due to their interaction with different targets, such as (intense) light pulses, atoms, clusters or bulk material. They are formed, in addition, if highly charged ions approach surfaces and capture electrons at rather large distances. To explore the interaction of such hollow ions and their subsequent relaxation, photon spectra in different frequency regions have been measured and compared to calculations. To support these and related measurements, we here show within the framework of the Jena Atomic Calculator (Jac) how (additional) electrons in outer shells modify photon emission and lead to characteristic shifts in the observed spectra. Further, for highly charged Ar ions in KL

^{m} (m = 1 \dots 8)

configurations, we analyze the mean relaxation time for their stabilization into the different ground configurations. These examples demonstrate how a powerful and flexible toolbox such as Jac will be useful (and necessary) in order to model the photon and electron emission of ions as they occur not only near surfaces but also in astro-, atomic and plasma physics. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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5 pages, 233 KiB

Open AccessArticle

Comments on Computation of Free-Free Transitions in Atomic Physics

by Anand K. Bhatia and Joseph Sucher

Atoms 2022, 10(2), 35; https://doi.org/10.3390/atoms10020035 - 02 Apr 2022

Viewed by 1678

Abstract

The amplitude T for ‘free-free’ processes such as bremsstrahlung or photoabsorption by an electron in the continuum in the presence of an external field, is usually written as the matrix element of the radiation operator taken between two continuum states. However, unlike the [...] Read more.

The amplitude T for ‘free-free’ processes such as bremsstrahlung or photoabsorption by an electron in the continuum in the presence of an external field, is usually written as the matrix element of the radiation operator taken between two continuum states. However, unlike the case when at least one of the states is bound, as in radiative transitions, electron capture or the photo-effect, this expression contains unphysical term, proportional to a delta function, and is not really the physical amplitude

T_{p h y s}

. We first give an a priori definition of

T_{p h y s}

in terms of the scattering parts of the continuum functions, which does not have this delta function term and has an obvious interpretation in terms of time-ordered diagrams. We then show that when the formal amplitude T is modified by a long-distance cutoff, the modified form

T_{α}

approaches

T_{p h y s}

as the cutoff is removed. The modified form may be used as the basis for calculation and approximations without the need to introduce further cutoffs at a later stage. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

13 pages, 538 KiB

Open AccessArticle

Inelastic Processes in Strontium-Hydrogen Collisions and Their Impact on Non-LTE Calculations

by Svetlana A. Yakovleva, Andrey K. Belyaev and Lyudmila I. Mashonkina

Atoms 2022, 10(1), 33; https://doi.org/10.3390/atoms10010033 - 17 Mar 2022

Cited by 3 | Viewed by 1849

Abstract

Inelastic processes rate coefficients for low-energy Sr + H, Sr

^{+}

+ H

^{-}

, Sr

^{+}

+ H, and Sr

^{2 +}

+ H

^{-}

collisions are calculated using the multichannel quantum model approach. A total of 31 scattering channels of SrH [...] Read more.

Inelastic processes rate coefficients for low-energy Sr + H, Sr

^{+}

+ H

^{-}

, Sr

^{+}

+ H, and Sr

^{2 +}

+ H

^{-}

collisions are calculated using the multichannel quantum model approach. A total of 31 scattering channels of SrH

^{+}

and 17 scattering channels of SrH are considered. The partial cross sections and the partial rate coefficients are hence calculated for 1202 partial processes in total. Using new quantum data for Sr ii + H i collisions, we updated the model atom of Sr ii and performed the non-local thermodynamic equilibrium (non-LTE) calculations. We provide the non-LTE abundance corrections for the Sr ii resonance lines in two grids of model atmospheres, which are applicable to very metal-poor ([Fe/H]

\leq - 2

) dwarfs and giants. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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15 pages, 1909 KiB

Open AccessArticle

Study of Positron Impact Scattering from Methane and Silane Using an Analytically Obtained Static Potential with Correlation Polarization

by Dibyendu Mahato, Lalita Sharma and Rajesh Srivastava

Atoms 2021, 9(4), 113; https://doi.org/10.3390/atoms9040113 - 14 Dec 2021

Cited by 3 | Viewed by 2153

Abstract

A detailed study of positron impact elastic scattering from methane and silane is carried out using a model potential consisting of static and polarization potentials. The static potential for the molecular target is obtained analytically by using accurate Gaussian molecular wavefunctions. The molecular [...] Read more.

A detailed study of positron impact elastic scattering from methane and silane is carried out using a model potential consisting of static and polarization potentials. The static potential for the molecular target is obtained analytically by using accurate Gaussian molecular wavefunctions. The molecular orbitals are expressed as a linear combination of Gaussian atomic orbitals. Along with the analytically obtained static potential, a correlation polarization potential is also added to construct the model potential. Utilizing the model potential, the Schrödinger equation is solved using the partial wave phase shift analysis method, and the scattering amplitude is obtained in terms of the phase shifts. Thereafter, the differential, integrated and total cross sections are calculated. These cross-section results are compared with the previously reported measurements and theoretical calculations. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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14 pages, 3249 KiB

Open AccessArticle

Triply Differential Positron and Electron Impact Ionization of Argon: Systematic Features and Scaling

by R. D. DuBois and O. G. de Lucio

Atoms 2021, 9(4), 78; https://doi.org/10.3390/atoms9040078 - 11 Oct 2021

Cited by 5 | Viewed by 1239

Abstract

Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to [...] Read more.

Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to 0.31 a.u. The binary and recoil intensities are fitted using a double peak structure in both regions, which, for the present kinematic conditions, are unresolved. The fitted peak intensities and angular positions are shown to have systematic dependences as a function of the momentum transfer and kinematic emission angle, respectively, and illustrate projectile charge effects. A comparison with available theories is made where it is seen that the most notable differences include the fact that for the binary lobe, the observed intensity for emission angles around 100° is absent in the theories, and the theoretical predications overestimate the importance of recoil interactions. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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Review

Jump to: Research

40 pages, 10778 KiB

Open AccessReview

Mechanisms of Electron-Induced Chemistry in Molecular Ices

by Fabian Schmidt, Tobias Borrmann, Martin Philipp Mues, Sanna Benter, Petra Swiderek and Jan Hendrik Bredehöft

Atoms 2022, 10(1), 25; https://doi.org/10.3390/atoms10010025 - 21 Feb 2022

Cited by 4 | Viewed by 2716

Abstract

Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation [...] Read more.

Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation liberates from such materials an abundance of secondary electrons of which most have energies below 20 eV. These electrons efficiently trigger reactions when they attach to molecules or induce electronic excitation and further ionization. This review focuses on the present state of insight regarding the mechanisms of reactions induced by electrons with energies between 0 and 20 eV that lead to formation of larger products in binary ice layers consisting of small molecules (H₂O, CO, CH₃OH, NH₃, CH₄, C₂H₄, CH₃CN, C₂H₆) or some derivatives thereof (C₂H₅NH₂ and (C₂H₅)₂NH, CH₂=CHCH₃). It summarizes our approach to identify products and quantify their amounts based on thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments performed in ultrahigh vacuum (UHV). The overview of the results demonstrates that, although the initial electron-molecule interaction is a non-thermal process, product formation from the resulting reactive species is often governed by subsequent reactions that follow well-known thermal and radical-driven mechanisms of organic chemistry. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms, Molecules and Surfaces)

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