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Atoms, Volume 11, Issue 5 (May 2023) – 11 articles

Cover Story (view full-size image): Fine-structure resolved collision strengths are the key to understanding the excitation of atoms and ions by electron impact. These strengths not only determine the energy-dependent cross-sections but also the behavior of plasma in different environments. For access to the electron-impact excitation of multiplying and highly charged ions, we have expanded the Jena Atomic Calculator (JAC) for rapid computations of distorted-wave collision strengths. This extension makes JAC a powerful toolbox for computing level structures, decay rates, plasma rate coefficients or even the simulation of atomic cascades and photon emission spectra. View this paper
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33 pages, 484 KiB  
Review
Atomic Lifetimes of Astrophysical Interest in Ions of Fe
by Elmar Träbert
Atoms 2023, 11(5), 85; https://doi.org/10.3390/atoms11050085 - 22 May 2023
Cited by 1 | Viewed by 1209
Abstract
Multiply charged ions of iron dominate the EUV spectrum of the solar corona. For the interpretation of such spectra, data on both the atomic structure and the transition rate are essential, most of which are provided by theory and computation. The wavelengths of [...] Read more.
Multiply charged ions of iron dominate the EUV spectrum of the solar corona. For the interpretation of such spectra, data on both the atomic structure and the transition rate are essential, most of which are provided by theory and computation. The wavelengths of observed spectra are used to test the predicted energy level structure, while the line intensities depend on level lifetimes and branch fractions. A number of electric dipole and higher-order transition rates have been measured over the years in the laboratory, mostly by beam-foil spectroscopy, at heavy-ion storage rings, and at various ion traps. In this paper, the state of the knowledge base on level lifetimes in all ions of Fe is assessed, and the problems of further progress are outlined. Full article
(This article belongs to the Special Issue Atomic and Molecular Data in Astronomy and Astrophysics)
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14 pages, 1562 KiB  
Article
Attosecond Time Delay Trends across the Isoelectronic Noble Gas Sequence
by Brock Grafstrom and Alexandra S. Landsman
Atoms 2023, 11(5), 84; https://doi.org/10.3390/atoms11050084 - 15 May 2023
Cited by 1 | Viewed by 1149
Abstract
The analysis and measurement of Wigner time delays can provide detailed information about the electronic environment within and around atomic and molecular systems, with one the key differences being the lack of a long-range potential after a halogen ion undergoes photoionization. In this [...] Read more.
The analysis and measurement of Wigner time delays can provide detailed information about the electronic environment within and around atomic and molecular systems, with one the key differences being the lack of a long-range potential after a halogen ion undergoes photoionization. In this work, we use relativistic random-phase approximation to calculate the average Wigner delay from the highest occupied subshells of the atomic pairings (2p, 2s in Fluorine, Neon), (3p, 3s in Chlorine, Argon), (4p, 4s, 3d, in Bromine, Krypton), and (5p, 5s, 4d in Iodine, Xenon). The qualitative behaviors of the Wigner delays between the isoelectronic pairings were found to be similar in nature, with the only large differences occurring at photoelectron energies less than 20 eV and around Cooper minima. Interestingly, the relative shift in Wigner time delays between negatively charged halogens and noble gases decreases as atomic mass increases. All atomic pairings show large differences at low energies, with noble gas atoms showing large positive Wigner delays, while negatively charged halogen ions show negative delays. The implications for photoionization studies in halide-containing molecules is also discussed. Full article
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11 pages, 677 KiB  
Article
Stabilizing Frequency of a Diode Laser to a Reference Transition of Molecular Iodine through Modulation Transfer Spectroscopy
by Lakhi Sharma, Atish Roy, Subhasis Panja and Subhadeep De
Atoms 2023, 11(5), 83; https://doi.org/10.3390/atoms11050083 - 12 May 2023
Cited by 2 | Viewed by 1651
Abstract
We report the frequency stabilization of an external cavity diode laser (ECDL) to a reference molecular iodine (I2) transition at 13,531.18 cm−1 (739.03382 nm). Using the Modulation Transfer Spectroscopy (MTS) method for the highly sensitive detection of weak absorption signals, [...] Read more.
We report the frequency stabilization of an external cavity diode laser (ECDL) to a reference molecular iodine (I2) transition at 13,531.18 cm−1 (739.03382 nm). Using the Modulation Transfer Spectroscopy (MTS) method for the highly sensitive detection of weak absorption signals, the Doppler-free absorption peaks of I2 corresponding to the hot band transition R(78) (1–11) are resolved. The ECDL’s frequency is stabilized with respect to one of the lines lying within the reference absorption band. For this, the iodine vapor cell is heated to 450 °C and the corresponding circularly polarized pump and probe beam powers are maintained at 10 mW and 1 mW, respectively, to avoid power broadening. The short (100 ms) and long-term (50 h) linewidths of the frequency stabilized laser are measured to be 0.75(3) MHz and 0.5(2) MHz, respectively, whereas the natural linewidth of the specific I2-transitions lie within a range of tens of MHz. Full article
(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)
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16 pages, 562 KiB  
Article
Dynamics of Twisted Electron Impact Ionization of CH4 and NH3 Molecule
by Nikita Dhankhar, Neha and Rakesh Choubisa
Atoms 2023, 11(5), 82; https://doi.org/10.3390/atoms11050082 - 10 May 2023
Cited by 2 | Viewed by 1061
Abstract
Electron vortex beams (EVBs, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact [...] Read more.
Electron vortex beams (EVBs, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact ionization. In this communication, we present, in the first Born approximation (FBA), the angular profiles of the triple differential cross section (TDCS) for the (e, 2e) process on CH4 and NH3 molecular targets in the coplanar asymmetric geometry. We compare the TDCS of the EVB for different values of OAM number m with that of the plane wave. For a more realistic scenario, we investigate the average TDCS for macroscopic targets to explore the influence of the opening angle θp of the twisted electron beam on the TDCS. In addition, we also present the TDCS for the coherent superposition of two EVBs. The results demonstrate that the twisted (e, 2e) process retrieves the p-type character of the molecular orbitals, which is absent in the plane wave TDCS for the given kinematics. The results for the coherent superposition of two Bessel beams show the sensitivity of TDCS toward the OAM number m. Full article
(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)
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9 pages, 1706 KiB  
Communication
Electron Impact Ionization Cross-Section Maxima of Atoms
by Antônio Carlos Fontes dos Santos and Károly Tőkési
Atoms 2023, 11(5), 81; https://doi.org/10.3390/atoms11050081 - 08 May 2023
Cited by 3 | Viewed by 1326
Abstract
Using measured cross-sections and polarizability data, an empirical scaling law is extracted for the electron collision single-ionization cross-section maxima of neutral atoms. We found that the cross sections scale linearly with the target’s static polarizability. We confirm this observation using our present three-body [...] Read more.
Using measured cross-sections and polarizability data, an empirical scaling law is extracted for the electron collision single-ionization cross-section maxima of neutral atoms. We found that the cross sections scale linearly with the target’s static polarizability. We confirm this observation using our present three-body classical trajectory Monte Carlo simulations. Full article
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15 pages, 736 KiB  
Article
Collision Strengths of Astrophysical Interest for Multiply Charged Ions
by Stephan Fritzsche, Li-Guang Jiao, Yuan-Cheng Wang and Jozef E. Sienkiewicz
Atoms 2023, 11(5), 80; https://doi.org/10.3390/atoms11050080 - 06 May 2023
Cited by 2 | Viewed by 1493
Abstract
The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their [...] Read more.
The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their significance, however, little is known quantitatively about these processes for low- and medium-impact energies of, say, Ekin5000 eV of the free incident electron. To further explore the role of impact excitation, we here expanded Jac, the Jena Atomic Calculator, to the computation of distorted wave collision strengths for fine-structure-resolved, as well as configuration-averaged transitions. While we excluded the formation of dielectronic resonances, these tools can be readily applied for ions with a complex shell structure and by including the major relativistic contributions to these strengths. Detailed computations of the collision strengths are shown and explained for the impact excitation of lithium- and chlorine-like ions. When compared with other, well-correlated methods, good agreement was found, and hence, these tools will support studies of effective collision strengths for a wide range of electron impact energies, levels, and ionic charge states. Full article
(This article belongs to the Special Issue Atomic Processes for Plasma Modeling Applications)
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18 pages, 2330 KiB  
Article
Projectile Coherence Effects in Twisted Electron Ionization of Helium
by A. L. Harris
Atoms 2023, 11(5), 79; https://doi.org/10.3390/atoms11050079 - 03 May 2023
Cited by 1 | Viewed by 1536
Abstract
Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that [...] Read more.
Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts. Full article
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12 pages, 10083 KiB  
Article
Enhanced Acetone Sensing Based on Group-11 Metal (Cu, Ag, and Au) Nanoparticles Embedded in Graphitic Carbon Nitride (gCN)
by Nihal, Rahul Sharma, Navjot Kaur, Mamta Sharma, B. C. Choudhary and J. K. Goswamy
Atoms 2023, 11(5), 78; https://doi.org/10.3390/atoms11050078 - 01 May 2023
Viewed by 1835
Abstract
In this work, a group-11 metal nanoparticle-embedded, graphitic carbon nitride-based, resistive-type sensor was developed for room temperature acetone sensing. We synthesized pure and group-11 transition metal (Cu, Ag and Au) nanoparticles embedded in graphitic carbon nitride (gCN) by thermal polycondensation and chemical reduction [...] Read more.
In this work, a group-11 metal nanoparticle-embedded, graphitic carbon nitride-based, resistive-type sensor was developed for room temperature acetone sensing. We synthesized pure and group-11 transition metal (Cu, Ag and Au) nanoparticles embedded in graphitic carbon nitride (gCN) by thermal polycondensation and chemical reduction methods. The synthesized material was characterized using UV/visspectroscopy, FTIRspectroscopy, XRD, HRTEM, FESEM, and EDS techniques. Sensing properties such as response, response/recovery time, selectivity, and stability were calculated. This study confirms that Ag/gCN is the best material for room temperature sensing of acetone compared to Cu/gCN, Au/gCN, and pure gCN. The response of Ag/gCN for 20 ppm acetone at room temperature is 28%. The response/recovery time is 42.05/37.09 s. Moreover, the response of Ag/gCN is stable for 10 days. Full article
(This article belongs to the Special Issue Recent Advances in Atomic and Molecular Spectroscopy)
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11 pages, 736 KiB  
Article
Trapped Ideal Bose Gas with a Few Heavy Impurities
by Orest Hryhorchak and Volodymyr Pastukhov
Atoms 2023, 11(5), 77; https://doi.org/10.3390/atoms11050077 - 28 Apr 2023
Viewed by 853
Abstract
In this article, we formulate a general scheme for the calculation of the thermodynamic properties of an ideal Bose gas with one or two immersed static impurities, when the bosonic particles are trapped in a harmonic potential with either a quasi-1D or quasi-2D [...] Read more.
In this article, we formulate a general scheme for the calculation of the thermodynamic properties of an ideal Bose gas with one or two immersed static impurities, when the bosonic particles are trapped in a harmonic potential with either a quasi-1D or quasi-2D configuration. The binding energy of a single impurity and the medium-induced Casimir-like forces between the two impurities are numerically calculated for a wide range of temperatures and boson–impurity interaction strengths. Full article
(This article belongs to the Special Issue Recent Trends on Quantum Fluctuations in Ultra-Cold Quantum Gases)
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13 pages, 4448 KiB  
Article
Theoretical Investigation of Electron–Ion Recombination Process of Mg-like Gold
by Luyou Xie, Wenliang He, Shengbo Niu, Jinglin Rui, Yulong Ma and Chenzhong Dong
Atoms 2023, 11(5), 76; https://doi.org/10.3390/atoms11050076 - 23 Apr 2023
Viewed by 1215
Abstract
The L-shell dielectronic and trielectronic recombinations of highly charged Mg-like gold ions (Au67+) in the ground state 2s22p63s2 1S0 have been studied systematically. The recombination cross-sections and rate coefficients are carefully calculated [...] Read more.
The L-shell dielectronic and trielectronic recombinations of highly charged Mg-like gold ions (Au67+) in the ground state 2s22p63s2 1S0 have been studied systematically. The recombination cross-sections and rate coefficients are carefully calculated for ∆n = 1 (2s/2p → 3l) transitions using a flexible atomic code based on the relativistic configuration interaction method and considering the Breit and QED corrections. Detailed resonance energies and resonance strengths are presented for the stronger resonances of the LMn (n = 3–12) series. It is found that the contributions of the trielectronic recombination to the total cross-section is about 13.75%, which cannot be neglected. For convenience of application, the plasma rate coefficients are also calculated and fitted to a semiempirical formula, and in the calculations, the contributions from the higher excited resonance groups n ≥ 13 are evaluated by an extrapolation method, which is about 2.93% of the total rate coefficient. Full article
(This article belongs to the Special Issue 20th International Conference on the Physics of Highly Charged Ions)
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16 pages, 2603 KiB  
Article
Fragmentation Dynamics of CO2q+ (q = 2, 3) in Collisions with 1 MeV Proton
by Avijit Duley and Aditya. H. Kelkar
Atoms 2023, 11(5), 75; https://doi.org/10.3390/atoms11050075 - 23 Apr 2023
Viewed by 1301
Abstract
The fragmentation dynamics of the CO2q+ (q = 2, 3) molecular ions formed under the impact of 1 MeV protons is studied using a recoil ion momentum spectrometer equipped with a multi-hit time- and position-sensitive detector. Both two-body and three-body [...] Read more.
The fragmentation dynamics of the CO2q+ (q = 2, 3) molecular ions formed under the impact of 1 MeV protons is studied using a recoil ion momentum spectrometer equipped with a multi-hit time- and position-sensitive detector. Both two-body and three-body fragmentation channels arising from the doubly and triply ionized molecular ions of CO2 are identified and analyzed. Kinetic energy release (KER) distributions have been obtained for various channels. With the help of Dalitz plots and Newton diagrams concerted and sequential processes have been assigned to observed fragmentation channels. In addition, angular correlations are used to determine the molecular geometry of the precursor molecular ion. It is found that the symmetric breakup into C+ + O+ + O+ involves asymmetric stretching of the molecular bonds in CO23+ prior to dissociation via concerted decay implying the fact that collisions with 1 MeV proton induces an asynchronous decay in CO2. Full article
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