Search Results (513)

We investigate theoretically the 75 keV proton-impact ionization of atomic helium. The convoluted quasi-Sturmian approach is extended to treat, on an equal footing, both the direct mechanism and the electron capture to the continuum. This is achieved by proposing an ansatz of the Green’s function of the three-body Coulomb system $(e^{-},{He}^{+},p^{+})$ that is compatible with the well-known 3C correlated continuum wave function. The model that stems from this approximation, named $3\tilde{C}$, is tested numerically using parabolic Sturmian expansions. Calculations of fully differential cross sections are presented for different regimes of energy losses, namely for ejected electron energies below, nearly equal to, and above the cusp energy. Our results are compared with recent experimental measurements and other theoretical calculations. The proposed $3\tilde{C}$ model yields very encouraging results and paves the way towards a more advanced Lippmann–Schwinger approach based on the 3C model. Full article

We present fully relativistic calculations of integral cross sections and swarm transport properties for positron–radon scattering over a wide energy range (0–1000 eV) and reduced electric field range (0.01–1000 Td). Elastic (total, momentum-transfer and viscosity-transfer), discrete excitation, direct annihilation, positronium formation and positron-impact ionization cross sections are obtained using a complex relativistic optical potential method. Owing to the large atomic number of radon and the absence of experimental scattering data, a consistent relativistic treatment is essential. The present work provides the first fully relativistic, internally consistent cross-section dataset for positron swarms in radon gas. Using a multi-term solution of Boltzmann’s equation, steady-state transport coefficients are calculated and found to be strongly influenced by energy-dependent reactive loss, particularly positronium formation. Significant divergence between bulk and flux transport coefficients is observed, including non-monotonic bulk drift velocities and pronounced suppression of longitudinal bulk diffusion at intermediate fields (0.3–1000 Td). Time-dependent field-free calculations further quantify thermalization and annihilation dynamics through the evolution of the mean energy and $⟨Z_{\mathrm{eff}}⟩\left(t\right)$. These results provide a robust theoretical foundation for modelling positron transport and annihilation in radon and other heavy noble gases where relativistic and reactive effects are crucial. Full article

The development of modern society has intensified fossil fuel consumption, resulting in the depletion of oil resources and rising greenhouse gas emissions. In this context, the promotion of renewable alternatives in the transport sector has become essential, with Hydrotreated Vegetable Oil (HVO) emerging as a promising transitional fuel due to its compatibility with conventional diesel engines. To ensure proper engine operation and performance, the physical properties and chemical structure of HVO must be accurately characterized. Gas chromatography is commonly used for this purpose. While dedicated gas chromatography methods for HVO are available on specialized equipment, this study proposes a chromatographic method applicable to conventional gas chromatograph systems equipped with a flame ionization detector, enabling the analysis of HVO using commonly available laboratory equipment. The method was developed using commercially available HVO and pure n-alkanes (C₅–C₁₈) as reference compounds for component identification. The proposed approach enabled the estimation of carbon and hydrogen atom numbers in the analyzed fuel fractions and the determination of the stoichiometric air. The calculated values show good agreement with the literature data, confirming the reliability and applicability of the proposed boiling-point-based chromatographic method. Full article

There are some 300 naturally occurring nuclides. In addition, over 3000 radioactive isotopes have become known. The s(low) and r(apid) processes of neutron capture synthesize the nuclides heavier than iron. The synthesis, namely the increase in the atomic numbers Z, is actually governed by $\beta$ decays. A “flow” of successive neutron captures in the chart of the nuclides is intercepted by a nucleus whose $\beta$ decay half-life is short enough. In this review, I discuss the s-process exclusively. The neutron capture rate to be compared with the $\beta$ decay rate is represented by $\lambda =n_{\mathrm{n}}{v}_T<\sigma >$, where $n_{\mathrm{n}}$ is the neutron number density, $v_T$ is the neutron thermal velocity at the temperature T, and $<\sigma >$ is the Maxwellian averaged (around $v_T$) radiative neutron capture cross-section, which depends on the nucleus of interest. The classical analysis of the solar system abundances of nuclides leads to canonical combinations like $n_{\mathrm{n}}\sim {10}^8/{\mathrm{cm}}^3$ and $T\sim 3\times {10}^8$ K for the s-process. The s-process flow becomes intricate when the neutron capture and $\beta$ decay timescales are comparable, causing a branch of the flow. Subsequently, an evaluation of $\beta$ decay rates is required, which is difficult to do straightforwardly. In this review, I will discuss the historical developments and the current status of predicting $\beta$ decay rates under s-process environments (specified basically by temperature, density, and composition). Those conditions are inaccessible in the laboratory. Embedded in high-temperature environments, even a very massive atomic species could be highly ionized, and its atomic and nuclear excited states could be thermally populated. I will exemplify the consequent difficulties of $\beta$ decay rate evaluations for s-process studies. Full article

Perovskite solar cells (PSCs) have quickly achieved certified energy conversion efficiency reaching a certified record of 27.3% for single-junction cells, while having a low mass, thin-film form factor and high specific power, which are attractive for space energy systems. However, their long-term reliability in extraterrestrial environments is not adequately ensured by terrestrial qualification routes, and standardized space-related test protocols remain insufficiently developed. This review critically summarizes the current understanding of the degradation of PSCs under the influence of key environmental factors in space—ionizing and non-ionizing radiation, thermal vacuum exposure and thermal cycling, and ultraviolet radiation AM0, as well as atmospheric oxygen in low orbits. The central task of the work is to develop and justify the need to create specialized PSCs test protocols for space applications, since existing ground standards do not reflect the multifactorial nature and extreme orbital loads. It has been shown that thermal vacuum accelerates ion migration, interphase reactions, and degassing, while AM0 UV and atomic oxygen introduce additional photochemical and oxidative mechanisms of destruction; at the same time, stressors often act synergistically and are not detected by single-factor tests. Next, the limitations of the current IEC and ISOS are discussed and an approach to their expansion is formulated through the ISOS-T-Space and ISOS-LC-Space protocols, which integrate high vacuum, AM0 lighting, extended temperature ranges and controlled particle irradiation. It is concluded that the development and interlaboratory validation of such space-oriented protocols is a key condition for the correct qualification of PSCs and targeted optimization of materials and interfaces to meet the requirements of space energy. Full article

Differential ionization in ${\mathrm{C}}^{6+}+$He collisions is investigated using the single- and two-center wave-packet convergent close-coupling (WP-CCC) method for projectile energies of 1–6 MeV/u. We present three types of singly differential cross-sections (SDCSs) as functions of the ejection angle, ejection energy, and projectile scattering angle. The two-center framework incorporates couplings across all channels as well as electron correlations. Overall, both the single- and two-center WP-CCC results agree well with existing experimental and theoretical data (apart from the first Born ones) for the SDCS as a function of electron energy and the SDCS as a function of ejection angle, laying a foundation for investigation of doubly and fully differential ionization cross-sections. The cross-sections differential in the projectile scattering angle are presented for the first time. Full article

The increasing utilization of radiation in medicine, industry, and water purification highlights the need for efficient radiation-protection materials. This study investigates lead-free polymer composites based on high-density polyethylene (HDPE) filled with four metallic fillers: tungsten carbide (WC), molybdenum carbide (MoC), tungsten (W), and molybdenum (Mo) at 15 wt%. The objective is to evaluate their potential as alternatives to lead for shielding ionizing radiation. Mechanical performance was examined through tensile testing, while thermal stability was assessed based on the residual mass. Radiation-attenuation behavior was analyzed through linear and mass attenuation coefficients (µ and µₘ), radiation protection efficiency (RPE), half-value layer (HVL), mean free path (MFP), buildup factors (B), and effective atomic number (Z_eff) within the 47.9–248 keV energy range. The HDPE/W composite exhibited the greatest enhancement, with a mass attenuation coefficient (µₘ) 82.5% higher than that of pure HDPE, along with the highest linear attenuation coefficient (µ). Furthermore, tungsten-loaded samples achieved an RPE of 98.05% at 47.9 keV. The increased density, low B, and high Z_eff values collectively contribute to superior shielding performance. These findings indicate that HDPE filled with WC, MoC, W, and Mo are promising lead-free candidates for low-energy X-ray shielding applications. Full article

This study explored the electronic and structural tunability of fullerene (C₆₀) derivatives via functionalization with heteroatoms (O, S, Se) in mono-, di-, and tri-bridged configurations, including covalently modeled dimers. Calculations were performed using density functional theory (DFT) at the B3LYP/6-31G(d,p) level. Electronic descriptors such as total dipole moments (TDMs), HOMO–LUMO energy gaps (ΔE), global reactivity descriptors, total density of states (TDOS), molecular electrostatic potential (MESP) and non-covalent interactions (NCIs) were analyzed to elucidate how functionalization alters reactivity and stability. Key findings indicate that TDM increases and ΔE decreases in all functionalized C₆₀; for example, the TDM increased from 0 Debye for C₆₀ to 2.156 Debye for C₆₀–O–S–Se, and ΔE decreased from 2.762 eV (C₆₀) to 2.532 eV (C₆₀–Se), indicating enhanced reactivity. This aligns with global reactivity descriptors such as reduced ionization energy and hardness. Mapped MESP surfaces showed activation around heteroatom sites. Quantum theory of atoms in molecules (QTAIM) and NCI analyses revealed that while mono-bridged structures retain covalent linkages, dimeric systems such as C₆₀–O–C₆₀ and C₆₀–S–C₆₀ relax into weak, van der Waals-type interactions. OPDOS (overlap population density of states) highlighted antibonding character between the fragments in the conduction region. These results demonstrate that heteroatom functionalization enhances the electronic properties of C₆₀, making it a promising candidate for optoelectronic, organic photovoltaic, and sensor applications. Full article

Reaction OH + HI → I + H₂O (1) is an important atmospheric process transforming inactive HI into chemically active iodine atoms. In the present work, the reaction kinetics have been studied in a discharge fast-flow reactor coupled with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium and over a wide temperature range, T = 225–950 K. The reaction rate constant was determined both by a relative rate method (with the OH + Br₂ reaction as a reference) and by absolute measurements carried out under pseudo-first order conditions by monitoring the OH consumption kinetics in excess of hydrogen iodide. U-shaped temperature dependence was observed for the reaction rate constant, negative at low temperatures and positive at high temperatures. Recommended expression over the 225–950 K temperature range: k₁ = 1.13 × 10⁻¹¹ exp(354/T) + 6.93 × 10⁻¹¹ exp(−1010/T) cm³ molecule⁻¹ s⁻¹ or in the form of a modified Arrhenius expression, k₁ = 4.2 × 10⁻¹² × (T/298)^1.36 exp(666/T) cm³ molecule⁻¹ s⁻¹, with a total estimated uncertainty of 15% at all temperatures. The rate constant data obtained in this study are compared with the results of previous experimental works. Full article

This study elucidates the regulatory mechanisms of methoxy substitution and photoexcitation on the antioxidant properties of pterostilbene (PTE) versus resveratrol (RES), employing a combined approach of multi-reference calculations, density functional theory (DFT), time-dependent DFT (TD-DFT), and molecular docking. Spectral analysis indicates that trans isomers exhibit a significant redshift (~13 nm) and have oscillator strengths more than double those of cis isomers. A pivotal difference in photoisomerization kinetics was identified: methoxy substitution drastically lowers the isomerization barrier for RES, indicating that PTE is more readily photoisomerized. Regarding radical scavenging, thermodynamic data confirm that Hydrogen Atom Transfer (HAT) and Radical Adduct Formation (RAF) are spontaneous pathways; notably, the O1 site of trans-PTE serves as the optimal hydrogen donor. Conceptual DFT (CDFT) analysis reveals that photoexcitation triggers a dramatic electronic reconfiguration, particularly for cis-PTE, whose ionization potential in the S1 state drops sharply to 4.66 eV, accompanied by an increased softness of 0.38 eV⁻¹, rendering it a highly potent electron donor. Furthermore, molecular docking demonstrates that trans-PTE robustly occupies the Keap1 Kelch pocket (binding energy: −7.478 kcal/mol) to inhibit Nrf2 binding via its favorable planar geometry. Full article

By numerically solving the time-dependent Schrödinger equation (TDSE), we study the elementary excitation and ionization processes of atomic hydrogen on the same footing, which is irradiated by the two-color laser fields composed of a strong 400 nm pulse and a weak 800 nm pulse. We find that under different intensities of the 400 nm laser, the ionization and excitation probabilities exhibit completely distinct modulations with the variation in the intensity of the 800 nm laser. Electron energy spectra (EESs), including above-threshold ionization (ATI) peaks and below-threshold bound states, indicate that the involvement of Rydberg states and the shift of low-energy ATI peaks due to the increase in the ponderomotive energy are the primary causes of the above-mentioned modulation behavior. By virtue of a quantum-state-resolved numerical method, the angular-momentum-resolved EES reveal how the addition of the 800 nm laser field perturbs and modifies the strong, 400 nm dominated multiphoton excitation and ionization channels. Our study provides a flexible control strategy for multiphoton excitation and ionization in atoms and even molecules and further advances the understanding of the complex ultrafast dynamics driven by two-color femtosecond laser fields. Full article

In this paper, a novel ionization energy, $IE$, set theory-based organizational structure is suggested: (i) iso-protonic sets, ${}_{Z}IE$; (ii) iso-electronic sets, $I{E}_s$; and (iii) iso-ionic sets, $I{E}^{i+}$. A computational algorithm is proposed which was demonstrated on twenty-five iso-electronic $I{E}_s$-sets plotted vs. the nuclear charge, Z. The algorithm allows for: (i) the interpolative assessment of 162 new (not measured) IE values, with their uncertainties estimated by the Lagrange method, for ions from ₃₀Zn to ₄₁Nb; and (ii) effective atomic nuclear charge assessment. It is shown that the IE effective atomic nuclear charge assessment is strongly correlated with the Slater’s effective charge and Pauling electronegativity scale. Full article

Calcium phosphate–poly(methyl-methacrylate) composite layers have been synthetized on silicon substrates in magnetron sputtering discharge by adjusting the radio-frequency power. The electron energy distribution function measured at holder substrate position shifts to lower energies when the radio-frequency power applied to the magnetron source increases from 50 to 150 W and the poly(methyl-methacrylate) molecule dissociation is augmented. The optical emission spectral analysis indicated the dynamics of the excitation and ionization processes in the Ar–calcium phosphate–poly(methyl-methacrylate) plasma mixture, as well as the dissociation patterning of the polymer molecules. The Ca I, P I, and H_α atomic lines and CaO, PO, POH, CO, CH and C₂ molecular bands characteristic to the calcium phosphate and poly(methyl-methacrylate) decomposition were evidenced. At 150 W radio-frequency power a reduction in the polymer content in the composite layer volume was observed even if the α-CH₃ main chain and the C=O molecular bands are still present. More C-C/C-H, C-OH/C-O-C polymeric bonds were revealed at the layer surface, indicating the formation of plasma polymers. The Ca/P ratio changes from 1.72 to 1.9 at 50 to 150 W, respectively, maintaining the amorphous structure of the layers. In this power range, the transition of layer surface morphologies from grain-like to worm-like plasma polymer characteristics is connected to an increase in plasma ion density and layer thickness. Full article

The relative position of the oxime group within pharmaceutically relevant pyridinium oximes is a pivotal factor that governs their intrinsic physicochemical properties and their biological reactivity. However, studies providing in-depth, molecular-level insight into these structure–reactivity relationships are still limited. In this work, we present an integrated experimental and computational study of N-methylpyridinium-2-aldoxime chloride (PAM2-Cl), N-methylpyridinium-3-aldoxime iodide (PAM3-I), and N-methylpyridinium-4-aldoxime iodide (PAM4-I), aimed at elucidating discrete differences in their ionization behavior, electronic structure, σ-donor properties, and nucleophilicity. The crystal structure of PAM3-I was determined by X-ray diffraction. Comparative structural and spectroscopic (UV–Vis, NMR, IR) analyses elucidated the structural and electronic effects arising from the position of the oxime group. Kinetic studies of substitution reactions with aquapentacyanoferrate(II) in aqueous solution enabled the determination of pentacyano(PAM)ferrate(II) formation and dissociation rate constants, coordination modes, pK_a values of the coordinated ligands, complex stability constants, and σ-donating capabilities. The DFT-based analysis of atomic charge distribution transcended experimental limitations, offering a new perspective on electronic structure-related properties. This study presents the first side-by-side, internally consistent structure–reactivity map across PAM2, PAM3, and PAM4 isomers that triangulates crystallography, UV–Vis-derived pK_a values, substitution kinetics, and DFT descriptors in a single framework. Full article

Dielectronic recombination (DR) is widely recognized as a fundamental atomic process in many astrophysical and laboratory plasmas, where it plays a crucial role in determining ionization balance and level populations over a broad temperature range. Reliable DR resonance strengths and plasma rate coefficients for such plasma modeling can be computed using the Jena Atomic Calculator (JAC)—a relativistic code based on the multiconfiguration Dirac–Hartree–Fock (MCDHF) method. In this work, we investigate the DR of Li-like Ar¹⁵⁺ ions in their ground state (2s), focusing on resonances associated with the fine-structure core excitations $2s_{1/2}\to 2p_{1/2,3/2}$. The resulting fine-structure-resolved DR resonance strengths and plasma rate coefficients are in good agreement with recent high-resolution DR measurements of Ar¹⁵⁺ ions performed at the Main Cooler Storage Ring (CSRm) in Lanzhou, China. These results provide a stringent benchmark for JAC calculations and support their applicability in plasma modeling. Full article