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Atoms, Volume 11, Issue 4 (April 2023) – 13 articles

Cover Story (view full-size image): Herbig-Haro (HH) objects are bright, bow-shaped shock fronts produced in nebulae by high-speed jets from newly formed stars. This Hubble Space Telescope image shows the objects HH 203 and HH 204 in the Orion Nebula's active star formation region. Deep high-resolution spectra of HH 204 obtained by Méndez-Delgado et al. (2021, Astrophys. J., 918, 27) are rich in forbidden lines from iron and nickel. These spectra have recently been used by Mendoza et al. (2023, Atoms, 11, 63) to provide observational benchmarks to evaluate the accuracy of the radiative and collisional rates for singly and doubly ionized iron in nebular modeling. Iron abundance is key to determining depletion factors in dust grains' life cycle. View this paper
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13 pages, 882 KiB  
Article
Ab Initio Double-Differential Ionization Cross-Section Calculations in Antiproton–Helium Collisions
by Imre Ferenc Barna, Mihály András Pocsai and Károly Tőkési
Atoms 2023, 11(4), 74; https://doi.org/10.3390/atoms11040074 - 20 Apr 2023
Cited by 1 | Viewed by 980
Abstract
We present ionization cross-sections for antiproton and helium collisions based on an ab initio time-dependent coupled channel method. In our calculations, a finite basis set of regular helium Coulomb wave packets and Slater function were used. The semiclassical approximation was applied with the [...] Read more.
We present ionization cross-sections for antiproton and helium collisions based on an ab initio time-dependent coupled channel method. In our calculations, a finite basis set of regular helium Coulomb wave packets and Slater function were used. The semiclassical approximation was applied with the time-dependent Coulomb potential to describe the antiproton–electron interaction. Three different projectile energies were considered as 10, 50 and 100 keV. We found clear evidence for the formation of the anti-cusp in the differential distributions. Full article
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8 pages, 607 KiB  
Communication
Rydberg Interaction-Induced Distortion of the Autler–Townes Spectra in Cold Lithium Atoms
by Sergey Saakyan, Nikita Morozov, Vladimir Sautenkov and Boris B. Zelener
Atoms 2023, 11(4), 73; https://doi.org/10.3390/atoms11040073 - 13 Apr 2023
Cited by 1 | Viewed by 1112
Abstract
In this article, effects of the strong long-range interaction of Rydberg atoms on the Autler–Townes splitting spectrum are investigated. Preliminary results are obtained for various excitation times and Rydberg atom densities. The 2S1/2 and 2P1/2 [...] Read more.
In this article, effects of the strong long-range interaction of Rydberg atoms on the Autler–Townes splitting spectrum are investigated. Preliminary results are obtained for various excitation times and Rydberg atom densities. The 2S1/2 and 2P1/2 levels of lithium-7 are coupled with strong laser field and probed by another laser via excitation into a 70S Rydberg level. Interactions between Rydberg atoms excited by the probe beam lead to the broadening of the Autler–Townes spectra. At high concentrations of Rydberg atoms, a suppression of the excitation of the Autler–Townes peak at red detuning is observed. Full article
(This article belongs to the Special Issue Cold and Rydberg Atoms for Quantum Technologies)
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19 pages, 6377 KiB  
Article
Temporal Response of Atoms Trapped in an Optical Dipole Trap: A Primer on Quantum Computing Speed
by S. Baral, Raghavan K. Easwaran, J. Jose, Aarthi Ganesan and P. C. Deshmukh
Atoms 2023, 11(4), 72; https://doi.org/10.3390/atoms11040072 - 10 Apr 2023
Viewed by 1680
Abstract
An atom confined in an optical dipole trap is a promising candidate for a qubit. Analyzing the temporal response of such trapped atoms enables us to estimate the speed at which quantum computers operate. The present work models an atom in an optical [...] Read more.
An atom confined in an optical dipole trap is a promising candidate for a qubit. Analyzing the temporal response of such trapped atoms enables us to estimate the speed at which quantum computers operate. The present work models an atom in an optical dipole trap formed using crossed laser beams and further examines the photoionization time delay from such confined atoms. We study noble gas atoms, such as Ne (Z = 10), Ar (Z = 18), Kr (Z = 36), and Xe (Z = 54). The atoms are considered to be confined in an optical dipole trap using X-ray Free Electron Lasers (XFEL). The present work shows that the photoionization time delay of the trapped atoms is different compared with that of the free atoms. This analysis alerts us that while talking about the speed of quantum computing, the temporal response of the atoms in the trapped environment must also be accounted for. Full article
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19 pages, 1997 KiB  
Review
Indigenisation of the Quantum Clock: An Indispensable Tool for Modern Technologies
by Subhadeep De and Arijit Sharma
Atoms 2023, 11(4), 71; https://doi.org/10.3390/atoms11040071 - 10 Apr 2023
Cited by 2 | Viewed by 2484
Abstract
Time and frequency (T&F) measurement with unprecedented accuracy is the backbone for several sophisticated technologies, commensurate with the evolution of human civilisation in the 20th century in terms of communication, positioning, navigation, and precision timing. This necessity drove researchers in the early 1950s [...] Read more.
Time and frequency (T&F) measurement with unprecedented accuracy is the backbone for several sophisticated technologies, commensurate with the evolution of human civilisation in the 20th century in terms of communication, positioning, navigation, and precision timing. This necessity drove researchers in the early 1950s to build atomic clocks that have now evolved to a state-of-the-art level, operating at optical wavelengths as optical atomic clocks, which use cold and trapped samples of atomic/ionic species and various other sophisticated diagnostic test techniques. Such ultrahigh-precision accurate clocks have made it possible to probe fundamental aspects of science through incredibly sensitive measurements. On the other hand, they meet the T&F synchronisation standards for classical and emerging quantum technologies at the desired level of accuracy. Considering the impact of optical atomic clocks in the second quantum revolution (quantum 2.0), they have been identified as an indispensable critical technology in worldwide quantum missions, including in India. This article reviews the present international scenario regarding optical atomic clocks and their related technologies and draws a roadmap for their indigenisation over the next decade. Full article
(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)
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21 pages, 397 KiB  
Article
Fine-Tuning of Atomic Energies in Relativistic Multiconfiguration Calculations
by Yanting Li, Gediminas Gaigalas, Wenxian Li, Chongyang Chen and Per Jönsson
Atoms 2023, 11(4), 70; https://doi.org/10.3390/atoms11040070 - 08 Apr 2023
Cited by 2 | Viewed by 1287
Abstract
Ab initio calculations sometimes do not reproduce the experimentally observed energy separations at a high enough accuracy. Fine-tuning of diagonal elements of the Hamiltonian matrix is a process which seeks to ensure that calculated energy separations of the states that mix are in [...] Read more.
Ab initio calculations sometimes do not reproduce the experimentally observed energy separations at a high enough accuracy. Fine-tuning of diagonal elements of the Hamiltonian matrix is a process which seeks to ensure that calculated energy separations of the states that mix are in agreement with experiment. The process gives more accurate measures of the mixing than can be obtained in ab initio calculations. Fine-tuning requires the Hamiltonian matrix to be diagonally dominant, which is generally not the case for calculations based on jj-coupled configuration state functions. We show that this problem can be circumvented by a method that transforms the Hamiltonian in jj-coupling to a Hamiltonian in LSJ-coupling for which fine-tuning applies. The fine-tuned matrix is then transformed back to a Hamiltonian in jj-coupling. The implementation of the method into the General Relativistic Atomic Structure Package is described and test runs to validate the program operations are reported. The new method is applied to the computation of the 2s21S02s2p1,3P1 transitions in C III and to the computation of Rydberg transitions in B I, for which the 2s2p22S1/2 perturber enters the 2s2ns2S1/2 series. Improved convergence patterns and results are found compared with ab initio calculations. Full article
(This article belongs to the Special Issue The General Relativistic Atomic Structure Package—GRASP)
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15 pages, 6053 KiB  
Article
Resonance States of Negative Hydrogen-like Ions in Quantum Plasmas
by Suya Yao, Zishi Jiang and Sabyasachi Kar
Atoms 2023, 11(4), 69; https://doi.org/10.3390/atoms11040069 - 07 Apr 2023
Viewed by 1261
Abstract
We studied the 1Se and 1,3Po resonance states of negative hydrogen-like ions immersed in quantum plasmas. The exponential cosine screened Coulomb potential was considered to model the quantum plasma environment. The correlated exponential wave functions in which the exponents [...] Read more.
We studied the 1Se and 1,3Po resonance states of negative hydrogen-like ions immersed in quantum plasmas. The exponential cosine screened Coulomb potential was considered to model the quantum plasma environment. The correlated exponential wave functions in which the exponents were generated by a pseudo-random technique were applied to represent the correlation effects between the charged particles. The stabilization method was used to calculate the resonance parameters (position and width). The resonance parameters (position and width) for Ps, Mμ, π, 1H, D, T and H embedded in quantum plasmas are reported for various screening parameters. The 1Se resonance parameters for Mμ, π, 1H, D, T ions and 1,3 Po states for Ps, Mμ, π, 1H, D, T and H of the proposed systems are reported for the first time in the literature. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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369 pages, 1459 KiB  
Article
GRASP Manual for Users
by Per Jönsson, Gediminas Gaigalas, Charlotte Froese Fischer, Jacek Bieroń, Ian P. Grant, Tomas Brage, Jörgen Ekman, Michel Godefroid, Jon Grumer, Jiguang Li and Wenxian Li
Atoms 2023, 11(4), 68; https://doi.org/10.3390/atoms11040068 - 05 Apr 2023
Cited by 14 | Viewed by 3107
Abstract
grasp is a software package in Fortran 95, adapted to run in parallel under MPI, for research in atomic physics. The basic premise is that, given a wave function, any observed atomic property can be computed. Thus, the first step is always to [...] Read more.
grasp is a software package in Fortran 95, adapted to run in parallel under MPI, for research in atomic physics. The basic premise is that, given a wave function, any observed atomic property can be computed. Thus, the first step is always to determine a wave function. Different properties challenge the accuracy of the wave function in different ways. This software is distributed under the MIT Licence. Full article
(This article belongs to the Special Issue The General Relativistic Atomic Structure Package—GRASP)
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8 pages, 904 KiB  
Communication
Does Carrier Envelope Phase Affect the Ionization Site in a Neutral Diatomic Molecule?
by Alex Schimmoller, Harrison Pasquinilli and Alexandra S. Landsman
Atoms 2023, 11(4), 67; https://doi.org/10.3390/atoms11040067 - 04 Apr 2023
Cited by 1 | Viewed by 1204
Abstract
A recent work shows how to extract the ionization site of a neutral diatomic molecule by comparing Quantum Trajectory Monte Carlo (QTMC) simulations with experimental measurements of the final electron momenta distribution. This method was applied to an experiment using a 40-femtosecond infrared [...] Read more.
A recent work shows how to extract the ionization site of a neutral diatomic molecule by comparing Quantum Trajectory Monte Carlo (QTMC) simulations with experimental measurements of the final electron momenta distribution. This method was applied to an experiment using a 40-femtosecond infrared pulse, finding that a downfield atom is roughly twice as likely to be ionized as an upfield atom in a neutral nitrogen molecule. However, an open question remains as to whether an assumption of the zero carrier envelope phase (CEP) used in the above work is still valid for short, few-cycle pulses where the CEP can play a large role. Given experimentalists’ limited control over the CEP and its dramatic effect on electron momenta after ionization, it is desirable to see what influence the CEP may have in determining the ionization site. In this paper, we employ QTMC techniques to simulate strong-field ionization and electron propagation from neutral N2 using an intense 6-cycle laser pulse with various CEP values. Comparing simulated electron momenta to experimental data indicates that the ratio of down-to-upfield ions remains roughly 2:1 regardless of the CEP. This confirms that the ionization site of a neutral molecule is determined predominantly by the laser frequency and intensity, as well as the ground-state molecular wavefunction, and is largely independent of the CEP. Full article
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20 pages, 4477 KiB  
Article
L-Shell Photoionization of Magnesium-like Ions with New Results for Cl5+
by Jean-Paul Mosnier, Eugene T. Kennedy, Jean-Marc Bizau, Denis Cubaynes, Ségolène Guilbaud, Christophe Blancard, M. Fatih Hasoğlu and Thomas W. Gorczyca
Atoms 2023, 11(4), 66; https://doi.org/10.3390/atoms11040066 - 03 Apr 2023
Cited by 2 | Viewed by 1358
Abstract
This study reports on the absolute photoionization cross sections for the magnesium-like Cl5+ ion over the 190–370 eV photon energy range, corresponding to the L-shell (2s and 2p subshells) excitation regime. The experiments were performed using the Multi-Analysis Ion Apparatus (MAIA) on [...] Read more.
This study reports on the absolute photoionization cross sections for the magnesium-like Cl5+ ion over the 190–370 eV photon energy range, corresponding to the L-shell (2s and 2p subshells) excitation regime. The experiments were performed using the Multi-Analysis Ion Apparatus (MAIA) on the PLéIADES beamline at the SOLEIL synchrotron radiation storage ring facility. Single and double ionization ion yields, produced by photoionization of the 2p subshell of the Cl5+ ion from the 2p63s2 1S0 ground state and the 2p63s3p 3P0,1,2 metastable levels, were observed, as well as 2s excitations. Theoretical calculations of the photoionization cross sections using the Multi-Configuration Dirac-Fock and R-matrix approaches were carried out, and the results were compared with the experimental data. The Cl5+ results were examined within the overall evolution of L-shell excitation for the early members of the Mg-like isoelectronic sequence (Mg, Al+, Si2+, S4+, Cl5+). Characteristic photon energies for P3+ were estimated by interpolation. Full article
(This article belongs to the Special Issue Photoionization of Atoms)
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9 pages, 690 KiB  
Article
A Method to Measure Positron Beam Polarization Using Optically Polarized Atoms
by Joshua R. Machacek, Sean Hodgman, Stephen Buckman and T. J. Gay
Atoms 2023, 11(4), 65; https://doi.org/10.3390/atoms11040065 - 03 Apr 2023
Viewed by 1141
Abstract
We outline an experimental technique for measuring the degree of polarization of a positron beam using an optically pumped, spin-polarized Rb target. The technique is based on the production and measurement of the ortho- and para-positronium fractions through positron collisions with the Rb [...] Read more.
We outline an experimental technique for measuring the degree of polarization of a positron beam using an optically pumped, spin-polarized Rb target. The technique is based on the production and measurement of the ortho- and para-positronium fractions through positron collisions with the Rb atoms as a function of their polarization. Using realistic estimates for the cross sections and experimental parameters involved, we estimate that a polarization measurement with an uncertainty of 3% of the measured value can be achieved in an hour. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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8 pages, 510 KiB  
Communication
Shape and Satellite Studies of Highly Charged Ions X-ray Spectra Using Bayesian Methods
by Martino Trassinelli
Atoms 2023, 11(4), 64; https://doi.org/10.3390/atoms11040064 - 01 Apr 2023
Cited by 1 | Viewed by 980
Abstract
High-accuracy spectroscopy commonly requires dedicated investigation into the choice of spectral line modelling to avoid the introduction of unwanted systematic errors. For such a kind of problem, the analysis of χ2 and likelihood are normally implemented to choose among models. However, these [...] Read more.
High-accuracy spectroscopy commonly requires dedicated investigation into the choice of spectral line modelling to avoid the introduction of unwanted systematic errors. For such a kind of problem, the analysis of χ2 and likelihood are normally implemented to choose among models. However, these standard practices are affected by several problems and, in the first place, they are useless if there is no clear indication in favour of a specific model. Such issues are solved by Bayesian statistics, in the context of which a probability can be assigned to different hypotheses, i.e., models, from the analysis of the same set of data. Model probabilities are obtained from the integration of the likelihood function over the model parameter space with the evaluation of the so-called Bayesian evidence. Here, some practical applications are presented within the context of the analysis of recent high-accuracy X-ray spectroscopy data of highly charged uranium ion transitions. The method to determine the most plausible profile is discussed in detail. The study of the possible presence of satellite peaks is also presented. Full article
(This article belongs to the Special Issue 20th International Conference on the Physics of Highly Charged Ions)
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34 pages, 864 KiB  
Article
Atomic Data Assessment with PyNeb: Radiative and Electron Impact Excitation Rates for [Fe ii] and [Fe iii]
by Claudio Mendoza, José E. Méndez-Delgado, Manuel Bautista, Jorge García-Rojas and Christophe Morisset
Atoms 2023, 11(4), 63; https://doi.org/10.3390/atoms11040063 - 01 Apr 2023
Cited by 3 | Viewed by 1638
Abstract
We use the PyNeb 1.1.16 Python package to evaluate the atomic datasets available for the spectral modeling of [Fe ii] and [Fe iii], which list level energies, A-values, and effective collision strengths. Most datasets are reconstructed from the sources, and [...] Read more.
We use the PyNeb 1.1.16 Python package to evaluate the atomic datasets available for the spectral modeling of [Fe ii] and [Fe iii], which list level energies, A-values, and effective collision strengths. Most datasets are reconstructed from the sources, and new ones are incorporated to be compared with observed and measured benchmarks. For [Fe iii], we arrive at conclusive results that allow us to select the default datasets, while for [Fe ii], the conspicuous temperature dependency on the collisional data becomes a deterrent. This dependency is mainly due to the singularly low critical density of the 3d7a4F9/2 metastable level that strongly depends on both the radiative and collisional data, although the level populating by fluorescence pumping from the stellar continuum cannot be ruled out. A new version of PyNeb (1.1.17) is released containing the evaluated datasets. Full article
(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)
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16 pages, 1171 KiB  
Article
Cyanide Molecular Laser-Induced Breakdown Spectroscopy with Current Databases
by Christian G. Parigger
Atoms 2023, 11(4), 62; https://doi.org/10.3390/atoms11040062 - 01 Apr 2023
Viewed by 1319
Abstract
This work discusses diatomic molecular spectroscopy of laser-induced plasma and analysis of data records, specifically signatures of cyanide, CN. Line strength data from various databases are compared for simulation of the CN, B2Σ+X2Σ+, [...] Read more.
This work discusses diatomic molecular spectroscopy of laser-induced plasma and analysis of data records, specifically signatures of cyanide, CN. Line strength data from various databases are compared for simulation of the CN, B2Σ+X2Σ+, Δv=0 sequence. Of interest are recent predictions using an astrophysical database, i.e., ExoMol, a laser-induced fluorescence database, i.e., LIFBASE, and a program for simulating rotational, vibrational, and electronic spectra, i.e., PGOPHER. Cyanide spectra that are predicted from these databases are compared with line-strength data that have been in use by the author for the last three decades in the analysis of laser–plasma emission spectra. Comparisons with experimental laser–plasma records are communicated as well for spectral resolutions of 33 and 110 picometer. The accuracy of the CN line-strength data is better than one picometer. Laboratory experiments utilize 308 nm, 35 picosecond bursts within an overall 1 nanosecond pulse-width, and 1064 nm, 6 ns pulse-width radiation. Experimental results are compared with predictions. Differences of the databases are elaborated for equilibrium of rotational and vibrational modes and at an internal, molecular temperature of the order of 8,000 Kelvin. Applications of accurate CN data include, for example, combustion diagnosis, chemistry, and supersonic and hypersonic expansion diagnosis. The cyanide molecule is also of interest in the study of astrophysical phenomena. Full article
(This article belongs to the Special Issue Atomic and Molecular Data in Astronomy and Astrophysics)
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