Research

15 pages, 472 KiB

Open AccessArticle

by Abhishek Prashant, Meetu Luthra, Kanupriya Goswami, Anand Bharadvaja and Kasturi Lal Baluja

Atoms 2023, 11(3), 55; https://doi.org/10.3390/atoms11030055 - 10 Mar 2023

Viewed by 1060

The positron impact cross-sections of pyrimidine molecules are reported from 1 eV to 5000 eV. These cross-sections include differential elastic, integral elastic, and direct ionisation. The elastic cross-sections are computed using the single-centre expansion scheme whereas the direct ionisation cross-sections are obtained using [...] Read more.

The positron impact cross-sections of pyrimidine molecules are reported from 1 eV to 5000 eV. These cross-sections include differential elastic, integral elastic, and direct ionisation. The elastic cross-sections are computed using the single-centre expansion scheme whereas the direct ionisation cross-sections are obtained using the binary-encounter-Bethe formula. The integral and differential cross-sections exhibit consistency with the experimental and other theoretical results. The direct ionisation cross-sections, which are reported for the first time, are compared with the experimental inelastic cross-sections (the sum of excitation and ionisation) to assess the trends in theoretically computed ionisation cross-sections and with the corresponding results for the electrons. The incoherently summed elastic and ionisation cross-sections match very well with the total cross-sections after 40 eV indicating the minimal impact of the positronium formation and electronic excitation processes. Based on this study, we recommend that the experimental data of the inelastic cross-sections reported by Palihawadana et al. be revisited. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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12 pages, 348 KiB

Open AccessArticle

Many-Body and Single-Body Low-Energy Elastic Positron Scattering by Beryllium Atoms: From Ab Initio to Semiempirical Approaches

by Marcos V. Barp, Wagner Tenfen and Felipe Arretche

Atoms 2023, 11(1), 8; https://doi.org/10.3390/atoms11010008 - 04 Jan 2023

Cited by 2 | Viewed by 1847

Abstract

Positron scattering by beryllium atoms in the low-energy range (≤4.0 eV) was studied within ab initio and semiempirical frameworks. When interpreting the static dipole polarizability and the scattering length as representative quantities of the target and positron–atom correlations, the scattering observables obtained in [...] Read more.

Positron scattering by beryllium atoms in the low-energy range (≤4.0 eV) was studied within ab initio and semiempirical frameworks. When interpreting the static dipole polarizability and the scattering length as representative quantities of the target and positron–atom correlations, the scattering observables obtained in the ab initio calculation were extrapolated by applying a semiempirical approach. Our results ratify previous ones, since no Ramsauer minimum structures or shape resonances were found in the cross sections. The presence of a (

e^{+}, B e

) bound state was also identified as a function of the dipole polarizability. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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12 pages, 397 KiB

Open AccessArticle

Partial Ionization Cross Sections of Tungsten Hexafluoride Due to Electron Impact

by Kanupriya Goswami, Meetu Luthra, Anand Bharadvaja and Kasturi Lal Baluja

Atoms 2022, 10(4), 101; https://doi.org/10.3390/atoms10040101 - 25 Sep 2022

Cited by 3 | Viewed by 1287

Abstract

The ionization data of a neutral molecule are crucial to model the energy deposition and dissociative ionization process. We study theoretically the electron impact ionization process and report on the dissociative ionization cross sections of the tungsten hexafluoride cations invoking the modified-binary-encounter-Bethe model. [...] Read more.

The ionization data of a neutral molecule are crucial to model the energy deposition and dissociative ionization process. We study theoretically the electron impact ionization process and report on the dissociative ionization cross sections of the tungsten hexafluoride cations invoking the modified-binary-encounter-Bethe model. In this model, the binary-encounter-Bethe model is modified by applying the transformation to the binding energies of the molecular orbitals and then normalizing the partial ionization cross sections of the cations using the branching ratios. The normalization is performed at a particular energy and ensures that the branching ratios of different fragments are summed to unity. The model yielded satisfactory results for both the singly and doubly ionized ions. The approach validates the results of Basner et al. The advantages and limitations of this model are also discussed. This work corroborates the importance of mass spectrometry data in the proper understanding of the ionization process. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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42 pages, 1901 KiB

Open AccessArticle

Electron and Positron Scattering from Precious Metal Atoms in the eV to MeV Energy Range

by Doris H. Jakubassa-Amundsen, Abul Kalam Fazlul Haque, Md. Monirul Haque, Md. Masum Billah, Arun Kumar Basak, Bidhan Chandra Saha and Md. Alfaz Uddin

Atoms 2022, 10(3), 82; https://doi.org/10.3390/atoms10030082 - 11 Aug 2022

Cited by 4 | Viewed by 1742

Abstract

This article reports on the scattering of unpolarized and spin polarized electrons and positrons from

_{28}

Ni

^{58},_{29}

Cu

^{63},_{46}

Pd

^{108}

, and

_{78}

Pt

^{196}

, covering light to heavy precious metal targets. To cover the wide [...] Read more.

This article reports on the scattering of unpolarized and spin polarized electrons and positrons from

_{28}

Ni

^{58},_{29}

Cu

^{63},_{46}

Pd

^{108}

, and

_{78}

Pt

^{196}

, covering light to heavy precious metal targets. To cover the wide energy domain of 1 eV

\leq E_{i} \leq 300

MeV, Dirac partial-wave phase-shift analysis is employed, using a complex optical potential for

E_{i} \leq 1

MeV and a potential derived from the nuclear charge distribution for

E_{i} > 1

MeV. Results are presented for the differential and integral cross-sections, including elastic, momentum transfer, and viscosity cross-sections. In addition, the inelastic, ionization, and total (elastic + inelastic) cross-section results are provided, together with mean free path estimates. Moreover, the polarization correlations

S, T

, and U, which are sensitive to phase-dependent interference effects, are considered. Scaling laws with respect to collision energy, scattering angle, and nuclear charge number at ultrahigh energies are derived using the equivalence between elastic scattering and tip bremsstrahlung emission. In addition, a systematic analysis of the critical minima in the differential cross-section and the corresponding total polarization points in the Sherman function S is carried out. A comparison with existing experimental data and other theoretical findings is made in order to test the merit of the present approach in explaining details of the measurements. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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15 pages, 925 KiB

Open AccessArticle

Mass Spectrometry-Based Approach to Compute Electron-Impact Partial Ionization Cross-Sections of Methane, Water and Nitromethane from Threshold to 5 keV

by Meetu Luthra, Kanupriya Goswami, Ajay Kumar Arora, Anand Bharadvaja and Kasturi Lal Baluja

Atoms 2022, 10(3), 74; https://doi.org/10.3390/atoms10030074 - 14 Jul 2022

Cited by 3 | Viewed by 1859

Abstract

The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the [...] Read more.

The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the orbitals and the scaling of cross-sections using the electron ionization mass spectrometry data. The computed partial ionization cross-sections are consistent with the recommended data and are better than several experimental and theoretical results. The summed partial ionization cross-sections of different fragments also agree with the total ionization cross-sections obtained from BEB and the experimental data. This work highlights the utility of mass spectrometry in the modeling and interpretation of the ionization cross-section data. The limitations and the advantages of the modified form of the BEB model are also discussed. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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Graphical abstract

11 pages, 3011 KiB

Open AccessArticle

Low-Energy Electron Scattering from c-C₄F₈

by Dhanoj Gupta, Heechol Choi, Deuk-Chul Kwon, He Su, Mi-Young Song, Jung-Sik Yoon and Jonathan Tennyson

Atoms 2022, 10(2), 63; https://doi.org/10.3390/atoms10020063 - 14 Jun 2022

Cited by 1 | Viewed by 1826

Abstract

Electron collision cross-sections of c-C₄F₈ were investigated at low energies by using the R-matrix method. The static exchange (SE), static exchange with polarization (SEP), and close-coupling (CC) models of the R-matrix method were used for the calculation of the [...] Read more.

Electron collision cross-sections of c-C₄F₈ were investigated at low energies by using the R-matrix method. The static exchange (SE), static exchange with polarization (SEP), and close-coupling (CC) models of the R-matrix method were used for the calculation of the scattering cross-section. The shape resonance was detected with all the models at around 3~4 eV, and a Feshbach resonance was detected with the SEP model at 7.73 eV, in good agreement with the previous theoretical calculation. The resonance detected was also associated with the experimental dissociative electron attachment of c-C₄F₈, which displayed the resonances at the same energy range. The cross-sections calculated are important for plasma modeling and applications. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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19 pages, 1234 KiB

Open AccessArticle

The Binary-Encounter-Bethe Model for Computation of Singly Differential Cross Sections Due to Electron-Impact Ionization

by Pankaj Garkoti, Meetu Luthra, Kanupriya Goswami, Anand Bharadvaja and Kasturi Lal Baluja

Atoms 2022, 10(2), 60; https://doi.org/10.3390/atoms10020060 - 06 Jun 2022

Cited by 4 | Viewed by 2280

Abstract

In the present work, we assess the effectiveness of singly differential cross sections (SDCS) due to electron-impact ionization by invoking the binary-encounter-Bethe (BEB) model on various atomic and molecular targets. The computed results were compared with the experimental and theoretical data. A good [...] Read more.

In the present work, we assess the effectiveness of singly differential cross sections (SDCS) due to electron-impact ionization by invoking the binary-encounter-Bethe (BEB) model on various atomic and molecular targets. The computed results were compared with the experimental and theoretical data. A good agreement was observed between the present and the available results. This agreement improves as the incident energy of the projectile increases. The model can be applied to compute the SDCS for the ions produced due to the electron-impact dissociative ionization process and the average energy due to the secondary electrons. Both these quantities are of interest in plasma processing and radiation physics. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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Graphical abstract

23 pages, 11756 KiB

Open AccessArticle

Impact of Charge Migration and the Angle-Resolved Photoionization Time Delays of the Free and Confined Atom X@C₆₀

by Subhasish Saha, Sourav Banerjee and Jobin Jose

Atoms 2022, 10(2), 44; https://doi.org/10.3390/atoms10020044 - 30 Apr 2022

Cited by 1 | Viewed by 1825

Abstract

The present study is devoted to isolate and study the effect of charge migration on the photoionization from the X@C₆₀. The noble gas atoms, Ar, Kr, and Xe, are confined in the C₆₀ to investigate the impact of charge migration [...] Read more.

The present study is devoted to isolate and study the effect of charge migration on the photoionization from the X@C₆₀. The noble gas atoms, Ar, Kr, and Xe, are confined in the C₆₀ to investigate the impact of charge migration from the entrapped atom to the C₆₀ side. The present work concludes that the confinement oscillations in the photoionization features are amplified due to the charge migration. Further, the angle-resolved, spin average time delay is also investigated in the light of confinement. Features in the time delay due to the charge migration are more amplified relative to those in the cross-section or angular distribution. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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29 pages, 2192 KiB

Open AccessArticle

A Theoretical Study of Scattering of Electrons and Positrons by CO₂ Molecule

by M. Masum Billah, M. Mousumi Khatun, M. M. Haque, M. Yousuf Ali, Mahmudul H. Khandker, A. K. F. Haque, Hiroshi Watabe and M. Alfaz Uddin

Atoms 2022, 10(1), 31; https://doi.org/10.3390/atoms10010031 - 09 Mar 2022

Cited by 7 | Viewed by 2606

Abstract

This article presents a theoretical investigation of the differential, integrated, elastic, inelastic, total, momentum-transfer, and viscosity cross-sections, along with the total ionization cross-section, for elastically scattered electrons and positrons from a carbon dioxide (CO

_{2}

) molecule in the incident energy range of [...] Read more.

This article presents a theoretical investigation of the differential, integrated, elastic, inelastic, total, momentum-transfer, and viscosity cross-sections, along with the total ionization cross-section, for elastically scattered electrons and positrons from a carbon dioxide (CO

_{2}

) molecule in the incident energy range of 1 eV

\leq E_{i} \leq

1 MeV. In addition, for the first time, we report the spin polarization of e

^{\pm} -

CO

_{2}

scattering systems. The independent atom model (IAM) with screening correction (IAMS) using a complex optical potential was employed to solve the Dirac relativistic equation in partial-wave analysis. The comparison of our results with the available experimental data and other theoretical predictions shows a reasonable agreement in the intermediate- and high-energy regions. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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13 pages, 584 KiB

Open AccessArticle

Elastic and Inelastic Cross Sections for Low-Energy Electron Collisions with ClF Molecule Using the R-Matrix Method

by Monika Bassi, Anand Bharadvaja and Kasturi Lal Baluja

Atoms 2022, 10(1), 8; https://doi.org/10.3390/atoms10010008 - 19 Jan 2022

Cited by 1 | Viewed by 2177

Abstract

The ClF molecule belongs to an interhalogen family and is important in laser physics and condensed phase molecular dynamics. The elastic and excitation scattering cross sections are obtained in a fixed nuclei approximation using the UKRmol+ codes based on R-matrix formalism. The [...] Read more.

The ClF molecule belongs to an interhalogen family and is important in laser physics and condensed phase molecular dynamics. The elastic and excitation scattering cross sections are obtained in a fixed nuclei approximation using the UKRmol+ codes based on R-matrix formalism. The scattering calculations were performed in the static-exchange (SE), static-exchange-plus-polarisation (SEP), and close-coupling (CC) models. Three CC models with different target states were employed, namely, the 1-state, 5-states, and 12-states. In the CC model, the target states were represented by configuration interaction (CI) wavefunctions. A good agreement of dipole and quadrupole moments of the ground state was obtained with the experimental values, which indicates a good representation of the target modelling. The study predicted the existence of a shape resonance in the SE, SEP, and 5-states CC models. This resonance vanished in the 12-states CC model. The excitation cross sections from ground to the lowest two excited states were also reported. The elastic differential and momentum transfer cross sections were obtained in the 12-states CC models. The contribution of long-range interactions to elastic scattering was included via Born closure approach. The quantities like collision frequencies and rate coefficients were also presented over a wide range of electron temperatures. The ionization cross sections were computed using the binary-encounter-Bethe (BEB) model. The results were reported in

C_{2 v}

point group representation. Full article

(This article belongs to the Special Issue Many-Particle Dynamics in Collisions of Electrons, Positrons and Photons)

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