Atoms

14 pages, 749 KiB

Open AccessArticle

Modelling of X-Ray Spectra Originating from the He- and Li-like Ni Ions for Plasma Electron Temperature Diagnostics Purposes

by Karol Kozioł, Andrzej Brosławski and Jacek Rzadkiewicz

Atoms 2025, 13(2), 18; https://doi.org/10.3390/atoms13020018 - 9 Feb 2025

Abstract

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in [...] Read more.

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in a 1.585–1.620 Å wavelength range, originating from the He-like nickel ions and their dielectronic Li-, Be-, and B-like satellites for various electron temperature values in the 2 keV to 8 keV range. The presented results may be useful in improving the plasma electron temperature diagnostics based on nickel spectra. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

9 pages, 900 KiB

Open AccessArticle

Visible Light Spectroscopy of W¹⁴⁺ Ions in an Electron Beam Ion Trap

by Ben Niu, Zhaoying Chen, Jihui Chen, Yanting Li, Fangshi Jia, Bingli Li, Zhencen He, Jun Xiao, Yaming Zou and Ke Yao

Atoms 2025, 13(2), 17; https://doi.org/10.3390/atoms13020017 - 8 Feb 2025

Abstract

In this work, the visible lines of

W^{14 +}

ions in the wavelength range of 400–650 nm are investigated experimentally and theoretically. The experiments were performed in a low-energy electron beam ion trap. The simulated spectra of

W^{14 +}

ions (Nd-like) [...] Read more.

In this work, the visible lines of

W^{14 +}

ions in the wavelength range of 400–650 nm are investigated experimentally and theoretically. The experiments were performed in a low-energy electron beam ion trap. The simulated spectra of

W^{14 +}

ions (Nd-like) were obtained from atomic structure computations in combination with a collisional–radiative model. Overall, there is a reasonable similarity between the measurements and the results of the simulations, and most of the twelve observed spectral lines associated with

W^{14 +}

were tentatively identified. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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13 pages, 807 KiB

Open AccessArticle

High-Resolution Fourier Transform Spectra of Atomic Sulfur: Testing of Modified Quantum Defect Theory

by Vladislav E. Chernov, Nikolai L. Manakov, Alexei V. Meremianin, Alexander V. Naskidashvili, Svatopluk Civiš, Martin Ferus, Petr Kubelík, Ekaterina M. Zanozina and Oxana V. Zetkina

Atoms 2025, 13(2), 16; https://doi.org/10.3390/atoms13020016 - 8 Feb 2025

Abstract

QDT (quantum defect theory) is an effective technique for calculating processes involving highly excited (Rydberg) states of atoms, ions, and molecules with one valence electron outside filled shells, whose spectrum generally resembles a hydrogen-like atom’s spectrum. At the expense of some modification of [...] Read more.

QDT (quantum defect theory) is an effective technique for calculating processes involving highly excited (Rydberg) states of atoms, ions, and molecules with one valence electron outside filled shells, whose spectrum generally resembles a hydrogen-like atom’s spectrum. At the expense of some modification of QDT, in this paper, we extend its applicability to describe low- and intermediate-excited levels of atoms with more complex spectra (on the example of atomic sulfur S I). Transitions between just such states are responsible for the infrared (IR) spectra of atoms. While the quantum defects (QDs) of the highly excited Rydberg levels are determined by the energies of individual levels near the ionization threshold, the radial wave functions of low excited electronic states, in the framework of our modification of QDT, include the QD dependence on energy over a wide energy range; this dependence is determined from the whole spectral series. We show that, outside the atomic core domain, the electron radial functions calculated using modified semi-phenomenological QDT agree well with ab initio calculations. As another assessment of QDT accuracy, we show satisfactory agreement of the probabilities of dipole transitions in S I, taken from the NIST Atomic Spectra Database, with our QDT calculations. We perform an indirect experimental verification of QDT on the basis of spectra of S I in gas-discharge plasma measured by time-resolved high-resolution Fourier transfer spectroscopy (FTS). The Boltzmann plot built from our measured spectra demonstrates that QDT provides a satisfactory approximation for calculating the experimental lines’ intensities. Full article

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8 pages, 490 KiB

Open AccessArticle

Diagnostics of Spin-Polarized Ions at Storage Rings

by Anna Maiorova, Stephan Fritzsche, Andrey Surzhykov and Thomas Stöhlker

Atoms 2025, 13(2), 15; https://doi.org/10.3390/atoms13020015 - 4 Feb 2025

Abstract

Polarized heavy ions in storage rings are seen as a valuable tool for a wide range of research, from the study of spin effects in relativistic atomic collisions to the tests of the Standard Model. For forthcoming experiments, several important challenges need to [...] Read more.

Polarized heavy ions in storage rings are seen as a valuable tool for a wide range of research, from the study of spin effects in relativistic atomic collisions to the tests of the Standard Model. For forthcoming experiments, several important challenges need to be addressed to work efficiently with such ions. Apart from the production and preservation of ion polarization in storage rings, its measurement is an extremely important issue. In this contribution, we employ the radiative recombination (RR) of polarized electrons into the ground state of initially hydrogen-like, finally helium-like, ions as a probe process for beam diagnostics. Our theoretical study clearly demonstrates that the RR cross section, integrated over photon emission angles, is highly sensitive to both the degree and the direction of ion polarization. Since the (integrated) cross-section measurements are well established, the proposed method offers promising prospects for ion spin tomography at storage rings. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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9 pages, 521 KiB

Open AccessArticle

Experimental Cross Sections for Electron-Impact Single, Double, and Triple Ionization of La⁺

by B. Michel Döhring, Alexander Borovik, Jr., Florian Gocht, Kurt Huber and Stefan Schippers

Atoms 2025, 13(2), 14; https://doi.org/10.3390/atoms13020014 - 28 Jan 2025

Abstract

We report on new measurements of absolute cross sections for single, double, and triple electron-impact ionization of singly charged lanthanum ions. The resulting single and double ionization cross sections are in fair agreement with results from previous experimental work. In the present work, [...] Read more.

We report on new measurements of absolute cross sections for single, double, and triple electron-impact ionization of singly charged lanthanum ions. The resulting single and double ionization cross sections are in fair agreement with results from previous experimental work. In the present work, we extended the experimental range by a factor of two to approx. 2000 eV. To the best of our knowledge, there have been no previous measurements of triple ionization. The present work in progress aims to provide vitally needed atomic data for the astrophysical modeling of kilonovae. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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12 pages, 4934 KiB

Open AccessArticle

In Situ Study of the Temperature and Fluence Dependence of Yb²⁺ Luminescence in Yttrium Aluminum Garnet (YAG) Single Crystals

by Ruotong Chang, Yingjie Song, Hongtao Hu, Shasha Lv, Guangfu Wang and Menglin Qiu

Atoms 2025, 13(2), 13; https://doi.org/10.3390/atoms13020013 - 27 Jan 2025

Abstract

In this study, ion-beam-induced luminescence with 2 MeV H⁺ was used to excite YAG single crystals at different temperatures. Under several constant temperatures, the luminescence intensity of Yb²⁺ monotonically decreases with increasing fluence, eventually reaching approximately 35% of the initial intensity [...] Read more.

In this study, ion-beam-induced luminescence with 2 MeV H⁺ was used to excite YAG single crystals at different temperatures. Under several constant temperatures, the luminescence intensity of Yb²⁺ monotonically decreases with increasing fluence, eventually reaching approximately 35% of the initial intensity at a fluence of 3.5 × 10¹⁴ cm⁻². The nonmonotonic evolution behavior of Yb²⁺ luminescence intensity with temperature can be effectively described by the intermediate-state model under consecutive temperature variations. The presence of an intermediate state may be the primary cause of the negative thermal quenching of Yb²⁺ luminescence. Yb²⁺ luminescence intensity decreased to 60% of the initial intensity when the temperature was continuously varied in the 100–300 K range, although the peak position remained rather stable. The luminescence of Yb²⁺ exhibits good radiation resistance and thermal stability in the experimental temperature range. Full article

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9 pages, 799 KiB

Open AccessArticle

Single and Double Electron Capture by 1–16 keV Sn⁴⁺ Ions Colliding on H₂

by Emiel de Wit, Lennart Tinge, Klaas Bijlsma and Ronnie Hoekstra

Atoms 2025, 13(2), 12; https://doi.org/10.3390/atoms13020012 - 24 Jan 2025

Abstract

Single and double electron capture cross-sections for collisions of ¹¹⁸Sn⁴⁺ with molecular hydrogen have been measured in an energy range of 1 keV to 16 keV using a crossed-beam setup. The cross-sections are determined from measurements of charge-state-resolved ion currents obtained [...] Read more.

Single and double electron capture cross-sections for collisions of ¹¹⁸Sn⁴⁺ with molecular hydrogen have been measured in an energy range of 1 keV to 16 keV using a crossed-beam setup. The cross-sections are determined from measurements of charge-state-resolved ion currents obtained through a retarding field analyser. Remarkably, the single electron capture cross-sections for Sn⁴⁺ are more than a factor 3 smaller than the previously determined single electron capture cross-sections for Sn³+–H₂ collisions and the double electron capture cross-sections are only about 20% smaller than the single electron capture cross-sections. These results are understood on the basis of potential energy curve crossings. The first active curve crossings for the Sn⁴⁺–H₂ system happen at a relatively small internuclear distance of about 5.5 a.u., which should be compared to 8 a.u. for Sn³+ ions. Multi-channel Landau–Zener calculations have been performed for single electron capture and confirm these low cross-sections. The curve crossing for double electron capture by Sn⁴⁺ lies very close to the one for single electron capture, which may explain the single and double electron capture cross-sections being of similar magnitude. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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18 pages, 1928 KiB

Open AccessArticle

Calculated Transition Probabilities for Os VI Spectral Lines of Interest to Nuclear Fusion Research

by Maxime Brasseur, Patrick Palmeri and Pascal Quinet

Atoms 2025, 13(2), 11; https://doi.org/10.3390/atoms13020011 - 21 Jan 2025

Abstract

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock [...] Read more.

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock (MCDHF) methods, were used, with the detailed comparison of the results obtained with these two approaches allowing us to estimate the quality of the calculated radiative parameters. These atomic data, corresponding to 367 lines of five-times ionized osmium between 438.720 and 1486.275 Å, are expected to be useful for the analysis of the spectra emitted by fusion plasmas in which osmium could appear as a result of transmutation by the neutron bombardment of tungsten used as component of the reactor wall, such as the ITER divertor. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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6 pages, 259 KiB

Open AccessCommunication

Lithium-like O⁵⁺ Emission near 19 Å

by Jaan K. Lepson, Gregory V. Brown, Joel H. T. Clementson, Alexander J. Fairchild, Ming Feng Gu, Natalie Hell, Elmar Träbert and Peter Beiersdorfer

Atoms 2025, 13(2), 10; https://doi.org/10.3390/atoms13020010 - 21 Jan 2025

Abstract

Using a high-resolution grating spectrometer on the Livermore EBIT-I electron beam ion trap, we have measured three

n = 3, 4 \to n = 1

K-shell emission lines in lithium-like O

5^{+}

, which are situated near the O VIII Lyman- [...] Read more.

Using a high-resolution grating spectrometer on the Livermore EBIT-I electron beam ion trap, we have measured three

n = 3, 4 \to n = 1

K-shell emission lines in lithium-like O

5^{+}

, which are situated near the O VIII Lyman-

α

lines at 19 Å. Two of the resulting wavelengths agree well with the wavelengths of these lines we reported earlier, but the wavelength of the third line does not. In contrast, our new wavelengths now fully agree with those from resonant photo-absorption experiments on the PETRA III synchrotron facility. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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11 pages, 1763 KiB

Open AccessArticle

Density Functional Theory Study of Hydrogen Adsorption on Al-U Alloy Surfaces

by Xiaoting Wang, Min Guan, Duo You, Dong Xie, Mingxi Hou and Yongxiang Leng

Atoms 2025, 13(2), 9; https://doi.org/10.3390/atoms13020009 - 21 Jan 2025

Abstract

To better understand the hydrogen corrosion mechanism on uranium surfaces and assess the hydrogen penetration resistance of Al-U alloys, the adsorption of hydrogen atoms on U(110), Al(111), and nAl/U(110) alloy surfaces was systematically studied through density functional theory (DFT) calculations. The results reveal [...] Read more.

To better understand the hydrogen corrosion mechanism on uranium surfaces and assess the hydrogen penetration resistance of Al-U alloys, the adsorption of hydrogen atoms on U(110), Al(111), and nAl/U(110) alloy surfaces was systematically studied through density functional theory (DFT) calculations. The results reveal that when U is alloyed with Al, the adsorption behavior of H atom on its surface thereon changes greatly. Specifically, the adsorption energy of H decreases with increasing Al content, indicating a weakening of the interaction between the H atom and the surface. A correlation between binding strength and alloy composition was established using d-band center theory. The incorporation of Al atoms alters the electronic structure of the U(110) surface, shifting the d-band center of uranium atoms downward. This shift results in a weakened interaction between the adsorbed H atom and the alloy surface. Full article

(This article belongs to the Section Quantum Chemistry, Computational Chemistry and Molecular Physics)

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9 pages, 1173 KiB

Open AccessArticle

Cooperative Decay of N Atoms in a Ring Configuration

by Nicola Piovella

Atoms 2025, 13(1), 8; https://doi.org/10.3390/atoms13010008 - 16 Jan 2025

Abstract

We provide an analytic expression of the spectrum of the cooperative decay rate of N two-level atoms regularly distributed on a ring in the single-excitation configuration. The results are obtained first for the scalar model and then extended to the vectorial light model, [...] Read more.

We provide an analytic expression of the spectrum of the cooperative decay rate of N two-level atoms regularly distributed on a ring in the single-excitation configuration. The results are obtained first for the scalar model and then extended to the vectorial light model, assuming all the dipoles are aligned. Full article

(This article belongs to the Section Cold Atoms, Quantum Gases and Bose-Einstein Condensation)

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8 pages, 257 KiB

Open AccessArticle

The Feshbach Resonances Applied to the Calculation of Stark Broadening of Ionized Spectral Lines: An Example of Interdisciplinary Research

by Sylvie Sahal-Bréchot and Haykel Elabidi

Atoms 2025, 13(1), 7; https://doi.org/10.3390/atoms13010007 - 16 Jan 2025

Abstract

In the present paper, we revisit the determination of Feshbach resonances in the elastic and fine-structure cross-sections of the spectral lines of ionized atoms colliding with electrons. The Gailitis approximation will be recalled and used to calculate the Feshbach resonances. A historical point [...] Read more.

In the present paper, we revisit the determination of Feshbach resonances in the elastic and fine-structure cross-sections of the spectral lines of ionized atoms colliding with electrons. The Gailitis approximation will be recalled and used to calculate the Feshbach resonances. A historical point of view will be used, emphasizing the interest of interdisciplinary research, with a back and forth between physics and astrophysics. First, the theory of Feshbach (arising at end of the 1950s and beginning of the 1960s) resonances will be briefly recalled and applied to the calculation of the cross-sections. In the beginning of the 1970s, the insertion of Feshbach resonances in spectroscopic diagnostics calculations permitted researchers to interpret the intensities of solar coronal lines. Then, in the middle of the 1970s, this gave rise to the idea of including the Feshbach resonances in the calculation of electron impact broadening (the so-called “Stark” broadening) of isolated spectral lines of ionized atoms. Finally, in the recent example of the Stark broadening of the Mo VI

5 d {}^{2}D_{5 / 2} - 5 p {}^{2}{P °}_{3 / 2}

line, the S-matrices will be calculated using the semi-classical perturbation formalism and will be compared to those of the more recent quantum distorted wave formalism. Full article

12 pages, 617 KiB

Open AccessArticle

Exploring the Nuclear Chart via Precision Mass Spectrometry with the TITAN MR-TOF MS

by Annabelle Czihaly, Soenke Beck, Julian Bergmann, Callum L. Brown, Thomas Brunner, Timo Dickel, Jens Dilling, Eleanor Dunling, Jake Flowerdew, Danny Fusco, Leigh Graham, Zach Hockenbery, Chris Izzo, Andrew Jacobs, Brian Kootte, Yang Lan, Stephan Malbrunot-Ettenauer, Fernando Maldonado Millán, Ali Mollaebrahimi, Erich Leistenschneider, Eleni Marina Lykiardopoulou, Ish Mukul, Stefan F. Paul, Wolfgang R. Plaß, Moritz Pascal Reiter, Christoph Scheidenberger, James L. Tracy, Jr. and A. A. Kwiatkowski Show full author list Hide full author list

Atoms 2025, 13(1), 6; https://doi.org/10.3390/atoms13010006 - 9 Jan 2025

Abstract

Isotopes at the limits of nuclear existence are of great interest for their critical role in nuclear astrophysical reactions and their exotic structure. Experimentally, exotic nuclides are challenging to address due to their low production cross-sections, overwhelming amounts of contamination, and lifetimes of [...] Read more.

Isotopes at the limits of nuclear existence are of great interest for their critical role in nuclear astrophysical reactions and their exotic structure. Experimentally, exotic nuclides are challenging to address due to their low production cross-sections, overwhelming amounts of contamination, and lifetimes of typically less than a second. To this end, a Multiple-Reflection Time-of-Flight mass spectrometer at the TITAN-TRIUMF facility was built to determine atomic masses. This device is the preferred tool to work with exotic nuclides due to its ability to resolve the species of interest from contamination and short measurement cycle times, enabling mass measurements of isotopes with millisecond half-lives. With a relative precision of the order 10⁻⁷, we demonstrate why the TITAN MR-TOF MS is the tool of choice for precision mass surveys for nuclear structure and astrophysics. The capabilities of the device are showcased in this work, including new mass measurements of short-lived tin isotopes (^104–107Sn) approaching the proton dripline as well as ⁸⁹Zr, ⁹⁰Y, and ⁹¹Y. The last three illustrate how the broadband surveys of MR-TOF MS reach beyond the species of immediate interest. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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11 pages, 1889 KiB

Open AccessArticle

Chemical Lasers Based on Polyatomic Reaction Dynamics: Research of Vibrational Excitation in a Reactive

by José Daniel Sierra Murillo

Atoms 2025, 13(1), 5; https://doi.org/10.3390/atoms13010005 - 9 Jan 2025

Abstract

The research presented by the author investigates a polyatomic reaction occurring in the gas phase. This study employs the Quasi-Classical Trajectory (QCT) approach using the Wu–Schatz–Lendvay–Fang–Harding (WSLFH) potential energy surface (PES), recognized as one of the most reliable PES models for this type [...] Read more.

The research presented by the author investigates a polyatomic reaction occurring in the gas phase. This study employs the Quasi-Classical Trajectory (QCT) approach using the Wu–Schatz–Lendvay–Fang–Harding (WSLFH) potential energy surface (PES), recognized as one of the most reliable PES models for this type of analysis. The substantial sample size enables the derivation of detailed results that corroborate previous findings while also identifying potential objectives for future experimental work. The Gaussian Binning (GB) technique is utilized to more effectively highlight the variation in the total angular momentum (J′) of the excited product molecule, HOD*. A key aim of the study is to explore the reaction dynamics due to their importance in excitation and emission processes, which may contribute to the development of a chemical laser based on this reaction. Increasing the vibrational level, v, of one reactant, D₂, significantly enhances the excitation of HOD* and shifts the P(J′) distributions towards higher J′ values, while also broadening the distribution. Although the current research focuses on a few initial conditions, the author plans to extend the study to encompass a wider range of initial conditions within the reaction chamber of this type of chemical laser. Full article

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13 pages, 1408 KiB

Open AccessArticle

Cooper Pairs in 2D Trapped Atoms Interacting Through Finite-Range Potentials

by Erick Manuel Pineda-Ríos and Rosario Paredes

Atoms 2025, 13(1), 4; https://doi.org/10.3390/atoms13010004 - 7 Jan 2025

Abstract

This work deals with the key constituent behind the existence of superfluid states in ultracold fermionic gases confined in a harmonic trap in 2D, namely, the formation of Cooper pairs in the presence of a Fermi sea in inhomogeneous confinement. For a set [...] Read more.

This work deals with the key constituent behind the existence of superfluid states in ultracold fermionic gases confined in a harmonic trap in 2D, namely, the formation of Cooper pairs in the presence of a Fermi sea in inhomogeneous confinement. For a set of finite-range models representing particle–particle interaction, we first ascertain the simultaneity of the emergence of bound states and the divergence of the s-wave scattering length in 2D as a function of the interaction potential parameters in free space. Then, through the analysis of two particles interacting in 2D harmonic confinement, we evaluate the energy shift with respect to the discrete harmonic oscillator levels for both repulsive and attractive cases. All of these results are the basis for determining the energy gaps of Cooper pairs arising from two particles interacting in the presence of a Fermi sea consisting of particles immersed in a 2D harmonic trap. Full article

(This article belongs to the Special Issue Quantum Technologies with Cold Atoms)

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11 pages, 1434 KiB

Open AccessArticle

Emergence of Quantum Vortices in the Ionization of Helium by Proton Impact, and How to Measure Them

by Tamara A. Guarda, Francisco Navarrete and Raúl O. Barrachina

Atoms 2025, 13(1), 3; https://doi.org/10.3390/atoms13010003 - 6 Jan 2025

Abstract

This study investigates how the presence of quantum vortices affects the ionization cross-section of helium atoms by 75 keV proton impact, with special attention to the region near the electron capture to the continuum (ECC) cusp. It has been found that these vortices [...] Read more.

This study investigates how the presence of quantum vortices affects the ionization cross-section of helium atoms by 75 keV proton impact, with special attention to the region near the electron capture to the continuum (ECC) cusp. It has been found that these vortices cause a significant reduction in the intensity of the

{| T |}^{2}

distribution in the low-energy region of the ECC cusp, leading to a considerable distortion that facilitates its experimental determination. Furthermore, the analysis shows that one of the vortices coincides with the Thomas angle (a parameter coming from the classical ion-electron Thomas mechanism). Full article

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11 pages, 260 KiB

Open AccessArticle

Nuclear Hyperfine Mixing Effect in Highly Charged ²⁰⁵Pb Ions

by Wu Wang, Yong Li and Xu Wang

Atoms 2025, 13(1), 2; https://doi.org/10.3390/atoms13010002 - 3 Jan 2025

Abstract

In highly charged ions, significant nuclear hyperfine mixing (NHM) effects can arise when the electromagnetic field generated by the electrons interacts strongly with the nucleus, leading to mixing of nuclear states. While previous studies have primarily attributed the NHM effect to unpaired valence [...] Read more.

In highly charged ions, significant nuclear hyperfine mixing (NHM) effects can arise when the electromagnetic field generated by the electrons interacts strongly with the nucleus, leading to mixing of nuclear states. While previous studies have primarily attributed the NHM effect to unpaired valence electrons, we present a reformulation of the theoretical framework using dressed hyperfine states and investigate the NHM effect in ²⁰⁵Pb⁷⁶⁺, ²⁰⁵Pb⁷⁵⁺, ²⁰⁵Pb⁷⁴⁺, and ²⁰⁵Pb⁷³⁺ ions. Our numerical results show that significant NHM effects occurred in all of the studied ions, even in the absence of unpaired valence electrons in ²⁰⁵Pb⁷⁶⁺ and ²⁰⁵Pb⁷⁴⁺. We found that the lifetime of the isomeric state was reduced by 2–4 orders of magnitude compared with the bare ²⁰⁵Pb nucleus, depending on the charge state of the ion. These results indicate that it is the active valence electrons rather than unpaired electrons which play a key role in the NHM effect, thereby deepening our understanding of this phenomenon. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

17 pages, 481 KiB

Open AccessArticle

Angular Distributions and Polarization of Fluorescence in an XUV Pump–XUV Probe Scheme

by Cristian Iorga and Viorica Stancalie

Atoms 2025, 13(1), 1; https://doi.org/10.3390/atoms13010001 - 24 Dec 2024

Abstract

This work provides theoretical calculations of fluorescence angular distribution and polarization within an XUV pump–XUV probe scheme designed for determining ultra-short lifetimes of highly charged heavy ions. The initial pumping leads to a non-zero alignment in the excited levels. After the probing stage, [...] Read more.

This work provides theoretical calculations of fluorescence angular distribution and polarization within an XUV pump–XUV probe scheme designed for determining ultra-short lifetimes of highly charged heavy ions. The initial pumping leads to a non-zero alignment in the excited levels. After the probing stage, the anisotropies in angular distribution and polarization of subsequent fluorescence are significantly enhanced due to the existence of a previous alignment. Furthermore, two-photon sequential excitation from a ground state with zero angular momentum to a level with angular momentum one by two aligned linearly polarized photon beams is strictly prohibited by the selection rules and may be used as a diagnostic tool to determine beam misalignment. The present approach is based on the density matrix and statistical tensor framework. We provide the analytical form for the alignment parameters caused by successive photoexcitation either with linearly polarized photon beams, or with unpolarized photons. The analytical results can generally be used to compute angular distribution asymmetry parameters and linear polarization of subsequent fluorescence for a large array of atomic systems used in pump–probe experiments. Full article

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9 pages, 1256 KiB

Open AccessArticle

Double and Triple Photoionization of CCl₄

by Antônio Carlos Fontes dos Santos, Joselito Barbosa Maciel, Alexandre Braga Rocha and Gerardo Gerson Bezerra de Souza

Atoms 2024, 12(12), 74; https://doi.org/10.3390/atoms12120074 - 21 Dec 2024

Abstract

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, [...] Read more.

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, ab initio quantum mechanical calculations were done at multiconfigurational self-consistent and multireference configuration interaction to describe ground and inner-shell states; (3) Results: We have observed coincidences involving singly and doubly charged fragments coming from the doubly and triply ionized molecule. We have also found a well agreement between the quantum mechanical calculations and the total ion yield spectrum. It is shown that the Cl⁺ ion is the predominant product resulting from the fragmentation of the doubly and triply charged CCl₄ molecule. The CCl⁺ + Cl⁺ pair is the dominant coincidence in the spectra from valence up to the C 1s edge; (4) Conclusions: The kinetic energy of the fragments is compatible with the Coulomb explosion model. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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