Search Results (115)

Single electron capture in collisions involving neutral hydrogen atoms impacted by highly charged dressed projectiles is theoretically investigated using the distorted wave formalism. A series of continuum distorted wave approximations is employed to investigate the electron capture from neutral hydrogen atom impact by boron and carbon projectiles. The projectile potential is described using a two-parameter analytical Green–Sellin–Zachor (GSZ) model potential. The theoretical prediction of total cross sections are compared against other theories and experiments. We looked at a very broad range of collision energies, from 10 keV/u up to 10 MeV/u. In addition, the state-selective cross sections for boron ions are presented. Full article

A combined experimental and theoretical study is carried out on the single-electron capture process in He⁺–He collisions at energies ranging from 0.5 keV/u to 5 keV/u. Using cold target recoil ion momentum spectroscopy, we obtain state-selective cross sections and angular differential cross sections. Within the entire studied energy range, the dominant channel is the electron captured into the ground-state, and the relative contribution of the dominant channel shows a decreasing trend with increasing energy. The angular differential cross sections of ground-state capture exhibit obvious oscillatory structures. To understand the oscillatory structures of the differential cross sections, we also performed theoretical calculations using the two-center atomic orbital close-coupling method, which well reproduced the oscillatory structures. The results indicate that these structures are strongly correlated to the oscillatory structures of the impact parameter dependence of electron probability. Full article

In this work, a comprehensive theoretical investigation is carried out to explore the electronic and spectroscopic properties of selected diatomic molecular ions MgRb⁺ and SrRb⁺. Using high-level ab initio calculations based on a pseudopotential approach, along with large Gaussian basis sets and full valence configuration interaction (FCI), we accurately determine adiabatic potential energy curves, spectroscopic constants, transition dipole moments (TDMs), and permanent electric dipole moments (PDMs). To deepen our understanding of these systems, we calculate radiative lifetimes for vibrational levels in both ground and low-lying excited electronic states. This includes evaluating spontaneous and stimulated emission rates, as well as the effects of blackbody radiation. We also compute Franck–Condon factors and analyze photoassociation processes for both ions. Furthermore, to explore low-energy collisional dynamics, we investigate elastic scattering in the first excited states (2¹Σ⁺) describing the collision between the Ra atom and Mg⁺ or Sr⁺ ions. Our findings provide detailed insights into the theoretical electronic structure of these molecular ions, paving the way for future experimental studies in the field of cold and ultracold molecular ion physics. Full article

Systematic R-matrix calculations of electron-impact excitation for ions of astrophysical interest have been performed since 2007 for many iso-electronic sequences as part of the UK Atomic Process for Astrophysical Plasma (APAP) network. Rate coefficients for Maxwellian electron distributions have been provided and used extensively in the literature and many databases for astrophysics. Here, we provide averaged collision strengths to be used to model plasma where electrons are non-Maxwellian, which often occurs in laboratory and astrophysical plasma. We also provide many new Maxwellian-averaged collision strengths, which include important corrections to the published values. Recently, we made available the H- and He-like collision strengths. Here, we provide data for ions of the Li-, Be-, B-, C-, N-, O-, Ne-, Na-, and Mg-like sequences. Full article

Within the framework of classical dynamics, the impact of laser amplitude on the cross-collision between a linearly polarized intense laser pulse and a relativistic electron under tight focusing conditions was investigated via numerical simulation. As the laser amplitude intensifies, the z-axis oscillation trajectory of the electron elongates. The spatial radiation angular distribution of the electron transforms from a “hill shape” to a “comet shape”, and the radiation peak shifts toward the direction of smaller polar angle, with the radiation concentrating in the forward position. The time spectrum is symmetrical; the number of peaks is reduced from multiple peaks to three peaks; and the relative height of the main peak and secondary peaks increases, with the time distribution gradually concentrating, which can be regarded as an ultrashort attosecond single pulse. The spectrum exhibits a multi-peak distribution trend. When the laser amplitude is relatively strong, radiation with a more concentrated frequency range and better quality can be output. The above research findings are beneficial for generating X-rays of higher quality and can be applied in fields such as biomedicine and atomic physics. Full article

The line ratios in X-ray emission resulting from charge exchange between highly charged ions (HCIs) and neutral atoms are not only crucial for accurately modeling astrophysical X-ray emissions but also offer a unique perspective on the charge exchange processes happening during collisions. The K X-ray spectra following charge exchange between Mg¹¹⁺ and He are presented for a collision velocity of 1489 km/s (11.5 keV/amu). The spectra were measured by two Silicon Drift Detectors capable of resolving the Mg¹⁰⁺ Kα, Kβ, Kγ, and Kδ+ lines. The line intensity ratios of Kβ, Kγ, and Kδ+ relative to the Kα line, as well as the hardness ratio, were obtained. The experimental results were compared with the theoretical results from a cascade model that utilizes the state cross-sections produced by multichannel Landau–Zener (MCLZ) calculation. It was discovered that the K X-ray spectrum features can be reproduced well by MCLZ theory when the contributions of both single electron capture (SEC) and autoionizing double capture (ADC) processes are included. This finding implies that the ADC feeding mechanism is significant and should be taken into account for the X-ray emission during charge exchange between highly charged ions and multielectron atoms. Full article

Electromagnetic induction heating, which converts electromagnetic energy into thermal energy via electron-lattice collisions, and heat conduction heating, which transfers thermal energy through lattice vibrations, both have significant impacts on the solid-state precipitation behavior caused by atomic diffusion. This paper proposes a creep method based on heat conduction heating, which utilizes the turning point of negative creep to measure the isothermal transformation start curve of the γ′ phase in the alloy. The results are compared with the thermal expansion experiments under electromagnetic induction heating and simulations from the thermodynamic analysis software JMatPro. The results indicate that the nucleation incubation period of the γ′ phase in the creep experiment is longer, excluding the non-thermal effects of electricity, and more consistent with actual heat treatment conditions. The overlapping precipitation of other phases, such as M₂₃C₆ carbides at grain boundaries, reduces the γ′ phase’s fastest precipitation temperature determined by the creep and thermal expansion methods, thereby lowering the accuracy of the isothermal transformation curve. This study provides a reference for optimizing production processes and evaluating the service performance of precipitation-strengthened iron–nickel-based alloys. Full article

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

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 $5\mathrm{d} {}^2\mathrm{D}_{5/2}-5\mathrm{p} {}^{2}P°_{3/2}$ 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

Positron physical-chemistry has been one important focus of scientific investigation of the last decades, however their low energy scattering by atoms and molecules still offers many questions to be answered, as the low angle scattering effects on the measured cross sections and how the degree of target polarization manifest in the comparison between theoretical and experimental results. In this work, we investigate low energy positron collisions by H₂ molecules, with particular attention to the convergence of the polarization contribution on the scattering potential. The interaction between positron and molecule was represented by a model potential conceived from the composition of a free electron gas correlation term with an asymptotic polarization potential, obtained from perturbation theory. In particular, we investigated how polarization effects beyond the second order perturbation affect the scattering observables. Our results show that the model which includes up to the quadrupole polarization contribution presents better agreement to the recent experimental data when corrected for forward scattering effects, since they were measured from a transmission beam technique. The angular distributions were also examined through the comparison between our results to the folded differential cross sections measurements available in the literature. We propose a simple correction scheme to the experimental folded differential cross sections for energies below 1 eV which then, as we argue, favorably compares to the quadrupole polarization model. Finally, the comparison between our phase shifts and scattering lengths with recent full many body ab initio results that explicitly include virtual positronium effects suggests that these are intrisically included in the adopted model correlation potential. Full article

Using the optical interaction potential between an electron and a helium atom, we have calculated the momentum-transfer cross-section, collision frequency, and energy transfer rate during elastic electron–helium scattering, focusing on energies up to the ionization threshold of helium (24.6 eV). The interaction potential includes static, polarization, and exchange contributions, accurately representing the scattering process in this range. The optical potential method is well-suited for this analysis, as it effectively reduces the complexity of multiparticle interactions while maintaining the essential physics of elastic scattering. The calculated collision frequency as a function of energy exhibits a distinct maximum near 5 eV, consistent with experimental observations, which has not been captured in earlier theoretical studies. The energy transfer rate, derived using the effective collision frequency, demonstrates efficient energy exchange at low electron energies, with a gradual decline as the energy approaches the ionization threshold. These findings offer critical insights into plasma processes in the diverter region of tokamaks, where helium atoms play a significant role, and contribute to modeling energy transport properties such as electron mobility and temperature equilibrium. The results can serve as a valuable reference for plasma simulations and fusion research applications. Full article

For many disciplines of science, all conceivable collisional cross-sections and reactions must be precisely known. Although recent decades have seen a trial of large-scale research to obtain such data, many essential atomic and molecular cross-section data are still missing, and the reliability of the existing cross-sections has to be validated. In this paper, we present projectile ionization, electron capture, and system breakdown cross-sections in carbon (C⁵⁺) ions and lithium (Li²⁺) ion collisions with atomic hydrogen based on the Monte Carlo models of classical and quasi-classical trajectories. According to our expectation, the QCTMC results show higher results in comparison to standard CTMC data, emphasizing the role of the Heisenberg correction constraint, especially in the low-energy regime. On the other hand, at high energy, the Heisenberg correction term has less influence as the projectile momentum increases. We present the total cross-sections of projectile ionization, electron capture, and system breakdown in C⁵⁺ ions and Li²⁺ ion collisions with atomic hydrogen in the impact energy range from 10 keV to 160 keV, which is of interest in astrophysical plasmas, atmospheric sciences, plasma laboratories, and fusion research. Full article

Nowadays, self-healing materials have been studied actively in electronics, soft robotics, aerospace, and automobiles because they can prolong the life span of the materials. However, overcoming the trade-off relationship between mechanical properties and self-healing performance is challenging. Herein, graphene oxide-polyaniline (GO-PANI) filler was introduced to overcome this challenge because GO has a highly excellent modulus, and nitrogen atoms in PANI can endow a self-healing ability through hydrogen bonds. Aside from the hydrogen bond in PANI, the hydrogen bond in the carbonyl group and the disulfide exchange bond in the epoxy matrix also helped the materials heal efficiently. Therefore, the modulus of SV-GPN1 (Self-healing Vitrimer-GO-PANI1) reached 770 MPa, and a 65.0% healing efficiency was demonstrated. The modulus and self-healing efficiency were enhanced after adding GO-PANI filler. The self-healing ability, however, deteriorated when adding more GO-PANI filler because it hindered the collision between the molecules. Meanwhile, SV-GPN1 was excellent in reproducibility, which was proven by the experiment that 16.50 mm thick SV-GPN1 also displayed a self-healing ability. Thus, SV-GPN1 can be applied to structural materials in industries like aerospace because of its self-healing ability, excellent modulus, and reproducibility. Full article

Indium phosphide (InP) is an excellent material used in space electronic devices due to its direct band gap, high electron mobility, and high radiation resistance. Displacement damage in InP, such as vacancies, interstitials, and clusters, induced by cosmic particles can lead to the serious degradation of InP devices. In this work, the analytical bond order potential of InP is modified with the short-range repulsive potential, and the hybrid potential is verified for its reliability to simulate the atomic cascade collisions. By using molecular dynamics simulations with the modified potential, the primary damage defects evolution of InP caused by 1–10 keV primary knock-on atoms (PKAs) are studied. The effects of electronic energy loss are also considered in our research. The results show that the addition of electronic stopping loss reduces the number of point defects and weakens the damage regions. The reduction rates of point defects caused by electronic energy loss at the stable state are 32.2% and 27.4% for 10 keV In-PKA and P-PKA, respectively. In addition, the effects of electronic energy loss can lead to an extreme decline in the number of medium clusters, cause large clusters to vanish, and make the small clusters dominant damage products in InP. These findings are helpful to explain the radiation-induced damage mechanism of InP and expand the application of InP devices. Full article

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. Chem. Phys. 1975, 10, 235–259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the negative ions formed in K + SF₆ collisions, in a wide energy range from 10.7 up to 213.1 eV in the centre-of-mass frame, show that the main anion is assigned to SF₅⁻ and contributing to more than 70% of the total ion yield, followed by the non-dissociated parent anion SF₆⁻ and F⁻. Other less intense anions amounting to <20% are assigned to SF₃⁻ and F₂⁻, while a trace contribution at 32u is tentatively assigned to S⁻ formation, although the rather complex intramolecular energy redistribution within the temporary negative ion is formed during the collision. An energy loss spectrum of potassium cation post-collision is recorded showing features that have been assigned with the help of theoretical calculations. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom are performed to support the experimental findings. Apart from the role of the different resonances participating in the formation of different anions, the role of higher-lying electronic-excited states of Rydberg character are noted. Full article