The expanding ejecta of binary neutron star mergers (NSMs) have been proven to be the ideal site for the production of lanthanides via rapid neutron capture (r-process) nucleosynthesis. However, identifying specific atomic absorption and emission features in kilonova spectra and linking them with individual elements remains significant challenges [1,2].

One of the primary obstacles is the lack of comprehensive collisional atomic data for modelling the late nebular epochs (> 4 days post-merger). While it is a reasonable approximation to assume that the ejecta is in local thermodynamic equilibrium (LTE) and that atomic absorption processes dominate in the early hours (< 1 day after the NSM), it is not possible to assume LTE for nebular epochs. During these late stages, relevant processes include photoionization, ionization, excitation by electron impact, and electronic recombination [3].

In this work, we address this gap by benchmarking electron-impact excitation collision strengths and line emissivities for Au and Pt against the existing literature [4,5], using the Flexible Atomic Code’s distorted-wave (DW) method [6]. Owing to its lower computational cost, the DW approach enables systematic calculations across the lanthanides, for which we report the results. We also present luminosity predictions derived from our atomic data [7]. Together, these calculations refine non-LTE spectral models, improving the interpretation of kilonova spectra and the tracing of heavy-element production.

[1] Nanae Domoto et al 2022 ApJ 939 8

[2] A Flörs et al 2023 MNRAS, Volume 524, Issue 2

[3] Quentin Pognan et al 2022 MNRAS Volume 513, Issue 4

[4] Michael McCann et al 2022, MRNAS 509(4):4723

[5] S. J. Bromley et al, 2023, ApJ 268 22

[6] M. F. Gu, “The Flexible Atomic Code,” J Phys 86(5):675 (2008)

[7] M McCann et al, 2025, MNRAS, Volume 538, Issue 1

The study of r-process elements, such as barium (Ba) and strontium (Sr), is key to understanding the formation of heavy elements in the Universe. More precisely, the hyperfine structure (HFS) of their atomic levels is commonly used by astrophysicists to determine abundances via spectral line modeling. Using the Multiconfiguration Dirac–Hartree–Fock (MCDHF) method as implemented in the General Relativistic Atomic Structure Package (GRASP) code, the magnetic dipole and electric quadrupole hyperfine structure constants were determined for the first excited states of Ba II isotopes, as well as for Ba I and Sr II isotopes to monitor the robustness of the developed model. New code developments, such as the use of natural orbitals, the addition of polarization effects and the use of Configuration State Function Generators (CSFGs) as implemented in GRASPG, were tested for these heavy elements. The developed strategy allowed us to achieve encouraging results, with little disagreement with experimental data for all studied level except ²D_5/2 in the first Ba II isotope. This disagreement was observed in another Ba II isotope as well as in Sr II. However, it emerged that the adopted strategy could not describe all the physics crucial for the Ba I states studied, with disagreements reaching up to 70%. This limitation necessitates the introduction of more intensive work employing a multireference (MR) approach to describe configuration mixing. Such efforts are expected to yield improved agreement with experimental values and outcomes from other theoretical computations. Nevertheless, the adopted strategy continues to serve as a valuable benchmark for comparing the MCDHF method with other theoretical approaches.

Abstract

The principles of atomic structure and spectroscopy form the cornerstone of modern biochemical research, offering deep insights into the composition, dynamics, and function of biomolecules. Theoretical models describing atomic and electronic structures—such as quantum mechanics and orbital theory—explain how atoms interact within biological macromolecules and influence biochemical reactivity. Experimental spectroscopic techniques derived from these theories, including UV–Visible, infrared (IR), nuclear magnetic resonance (NMR), fluorescence, and atomic absorption spectroscopy, provide powerful tools for structural elucidation, enzyme characterization, and metabolic profiling. This review bridges theoretical understanding with experimental practice, highlighting how atomic and spectral analysis enables precise detection of trace elements, investigation of metal–protein complexes, and monitoring of biochemical transformations. By integrating atomic theory and spectroscopic experimentation, this work underscores their pivotal role in advancing molecular biochemistry and biomedical science.

Accurate modeling of kilonova spectra, particularly during the late nebular phases (> 4 days post-merger) dominated by non-local thermodynamic equilibrium (non-LTE) processes [1, 2], demands detailed collisional atomic data for r process elements like lanthanides. While electron impact excitation (EIE) proceeds via direct scattering, the indirect pathway of resonant excitation (RE) represents another crucial, complex mechanism. RE proceeds via electron capture into intermediate autoionizing states followed by radiative decay to a bound excited level. Calculating RE accurately is computationally intensive [3, 4], and the requisite atomic data have been largely unavailable for complex lanthanide ions, often leading to the omission of its contribution in astrophysical models despite its potential to dominate total EIE rates [5].

Continuing our systematic effort to generate accurate atomic data for lanthanides, we present large-scale calculations focusing specifically on quantifying the impact of RE on EIE collision strengths for multiple singly and doubly ionized species. We employ the fully relativistic distorted wave (DW) method within the Flexible Atomic Code (FAC) [6]. These calculations utilize improved atomic structures derived from optimized potentials [7] and calibrated energy levels [8]. The RE channels were incorporated via the Independent Process, Isolated Resonance DW framework (IPIRDW) [5].

Our results provide extensive new EIE datasets highlighting the RE contribution, demonstrating that this resonant pathway provides a substantial, often dominant, component to the total collision strength for many astrophysically relevant transitions in lanthanides under nebular kilonova conditions [3, 4]. This work supplies vital atomic data focused on the resonant channel, needed to significantly enhance the fidelity of non-LTE radiative transfer simulations and improve interpretations of late time kilonova spectra.

[1] Pognan et al. MNRAS 510, 3806 (2022)
[2] Gillanders et al. MNRAS 529, 2918–2945 (2024)
[3] M McCann et al. MNRAS 538, 537–552 (2025)
[4] Leo P. Mulholland et al. JQSRT 345, 109545 (2025)
[5] Li et al. Chin. Phys. B. 24, 113401 (2015).
[6] Gu et al. Can. J. Phys. 86, 675 (2008)
[7] Ferreira da Silva et al., Phys. Rev. A 112(1), 012802 (2025)
[8] A. Flörs et al., arXiv:2507.07785 (2025)

Introduction

Metallic nanoclusters can be synthesized in a wide range of sizes and stoichiometries by incorporating coinage metals. Among the different sizes of nanoclusters, six atom clusters are of particular interest, as they represent the smallest experimentally realized species in both homo- and bimetallic forms, with or without passivating ligands. 2-(3-Methylureido)acetic acid is selected in this study due to its distinctive charge transfer characteristics.

Methods

All DFT computations were carried out with the Gaussian 16 package, employing B3LYP/ LANL2DZ. For the Ag₆ system, three possible configurations were used: metal cluster near to C=O as D1; near to COOH as D2; and near to NH as D3. Geometry optimizations were validated through harmonic vibrational frequency analyses, confirming the absence of imaginary modes.
Results and Discussion

For the MUA, the most reactive sites are O atoms and H atoms. The adsorption energies are -11.04, -6.73, and -4.70 kcal mol^-1 for configurations D1 to D3. The dipole moments (DMs) are varying in the order D1 (10.85) > D2 (10.30) >D3 (4.83). while that of MUA is 5.40 Debye, and for the D3 configuration, DM is less than that of MUA. The polarizability values of the complexes are significantly greater than that of MUA. The interaction between the Ag₆ cluster and drug is given by the separation distance of Ag to O8 as 2.3619 for D1; Ag to O15 separation of 2.4482 for D2; and Ag to N9 separation of 2.5539 Å for D3.
Conclusions

The interaction of MUA with Ag₆ has been comprehensively analyzed in terms of geometry, spectroscopy, polarization, and energetics. Overall, these results indicate that the MUA-Ag₆ system is a promising candidate for application in electronic devices. The D1 configuration gives the maximum adsorption energy.

Authors and Affiliations

Y.Sheena Mary : sheena@fatimacollege.net

Department of Physics, FMN College, Kollam, University of Kerala, Kerala, India

In Non-Local Thermodynamic Equilibrium (Non-LTE) plasmas, the ionization balance and excited-state populations are heavily determined by radiative (RR) and dielectronic (DR) recombination [1]. Accurate data for these processes are thus fundamental to the interpretation of spectral signatures. For kilonova-relevant ions, however, experimental data remains insufficient for spectral modelling, and therefore requires RR and DR data to be theoretically calculated [1,2].

To establish a reliable methodology, first, we perform a benchmark calculation on Pm-like tungsten (W XIV). Tungsten is extensively studied throughout its ionization sequence, providing a wealth of available data for comparison [3,4]. This particular charge state mimics the complicated open f-shell structure of key r-process elements and, consequently, the challenges that arise while performing this type of calculation [5].

In this work, we present primarily RR and DR rate coefficients for W XIV while including other relevant quantities: RR and photoionization cross-sections and precise DR resonance energies. All calculations were made using the well-established Flexible Atomic Code (FAC) [6], which handles the intricate ion structure at a relatively low computational cost. These results provide high confidence in our method, enabling us to subsequently address the lanthanide sequence.

[1] Singh, S. et al., A&A., 700, A110. 2025

[2] Pognan, Q. et al., MNRAS, 510, 3806. 2022

[3] Trzhaskovskaya, M.B. et al., At. Data Nucl. Data Tables, 139, 101389. 2021

[4] Trzhaskovskaya, M.B. et al., At. Data Nucl. Data Tables, 94, 71. 2008

[5] Preval, S. P. et al., J. Phys. B, 52, 025201. 2019

[6] M.F. Gu, Can. J. Phys., 86, 675. 2008

Electrons' interactions with matter give rise to a variety of atomic phenomena, including ionization, excitation, electron backscattering, and X-ray emission (Kanaya and Okayama 1972). In the present work, an experimental investigation was carried out to measure the bremsstrahlung (BS) yield produced by 10–25 keV electrons incident on a thick (0.1 mm) tungsten (Z = 74) target.

The objective of this study is to examine how the bremsstrahlung yield varies with electron energy, angle of incidence (α), and detection angle (θ). The experiment was conducted using a specially designed setup in which the electron beam and the detector were oriented orthogonally, with the target positioned at the center of the vacuum chamber facing the incident beam (Singh et al. 2018). The angle of incidence (α) was varied from 15° to 75°, measured with respect to the incident electron beam; correspondingly, the detection angle (θ) is described as (90° − α). The emitted X-rays were detected using a Si-PIN detector, and the resulting spectra were analyzed with MCA software to determine the photon yield distributions. The electron current was integrated directly on the target using a current integrator to obtain the total incident charge.

To validate the experimental results, the measured bremsstrahlung yields were normalized and compared with Monte Carlo simulations performed using the PENELOPE code (Salvat,F. 2015; Llovet and Salvat 2017). A comparison with the simulations provides insight into the angular dependence of the bremsstrahlung photon yield and the degree of symmetry or asymmetry with respect to the incidence angle.

The electronic stopping power of charged particles is a key parameter describing their slowing down, energy transfer, and penetration range in matter [1]. It plays a crucial role in diverse fields, including nuclear reactor design, ion beam analysis, ion implantation, radiation damage studies, molecular fragmentation, and hadron therapy. Particularly, the antiproton stopping power provides a stringent test for theoretical models operating under charge conjugation symmetry. The difference between proton and antiproton stopping powers, known as the Barkas effect, remains an active topic of research and discussion [2]. In this work, we present a non-perturbative model to describe the stopping power of transition metals (Ni, Cu, Ag, and Au) for low-energy antiprotons, based on the momentum distribution function of the target’s valence and subvalence electrons, combined with a fully relativistic solution of the electronic wave functions for transition metals with Z > 40. The model’s predictions are compared with available experimental data [3], revealing the expected linear dependence on impact velocity and reproducing the characteristic differences between proton and antiproton interactions.

[1] P. Sigmund, Particle Penetration and Radiation Effects Vol. 1, Springer-Verlag, Berlin, (2006).

[2] G. Massillon-JL et al., Phys. Rev. Lett 134, 076401 (2025).

[3] S. P. Møller et al., Phys. Rev. Lett 88, 193201 (2002).

We report an enhanced Classical Trajectory Monte Carlo (CTMC) approach developed to study state-selective charge exchange in collisions between multiply charged ions and H₂ molecules. The model combines two hydrogenic three-body formulations—originally designed to improve the H(1s) radial distribution—within the five-body CTMC framework introduced by Wood and Olson. The new schemes, termed E-CTMC and Z-CTMC, extend the electronic density of the target to larger distances, providing a more accurate representation of the molecular system. Calculations for Ne⁹⁺ and O⁶⁺ projectiles at intermediate and low impact energies are benchmarked against recent laboratory data and the Multichannel Landau–Zener method. The Z-CTMC approach reproduces the observed energy-dependent shift of the most populated n levels, showing the closest overall agreement with the experiments. Complementary simulations for different projectiles show that discrepancies among the CTMC variants grow with increasing projectile charge and lower impact energies, emphasizing the need for further experimental measurements involving highly charged ions. The present formulation offers a consistent framework for analyzing charge-exchange processes relevant to laboratory and astrophysical plasmas.

Work at IFISUR was supported by Grant No. PGI 24/F084 (UNS), Argentina.

Introduction: Accurate laboratory atomic data on spectral lines’ wavelengths, energy levels, and transition probabilities (or oscillator strengths) are inevitably important for several research fields and applications, for example, in the field of astrophysics and plasma physics, and for fundamental and technological applications, in which spectra and their modeling are a part. However, most of the laboratory data (experimental and theoretical) are often present in dissimilar formats, widely dispersed/scattered in the literature, and the literature may contain several values for a quantity that disagree greatly, leading to debate about what is best, most reliable, and final value. Critical evaluations of these data sets play a significant role in such cases.

Methods: Several statistical tools and techniques are available to compare and evaluate data from different sources, including modern-level optimization schemes such as LOPT. For theoretical support, extended HFR calculations were performed using Cowan’s codes. For evaluation of the transition probabilities (TP), multiple comparison schemes are generally carried out based on their dS = (S₁/S₂) as a function of line-strengths for a set of transitions with similar accuracy.

Results and Discussion: This work focuses on comprehensive spectral data analysis and their evaluations, including theoretical TP evaluations on spectra of some selected atoms/ions that we have recently compiled, including C II, Au IV, Cs XI, and Kr VI, and Si II.

Conclusion: In this work, the shortcomings of the existing atomic data are discussed, and, accordingly, the importance of critical evaluation of atomic data is demonstrated with specific examples.