We present all-electron close-coupling calculations of cross sections for electron capture and target excitation occurring in 0.25-200 keV/u He+-H collisions. We show overall good agreements with available experimental data for total electron capture, n = 2 target excitation, and related H a emission. We especially focus on n l-selective capture and excitation processes and critically compare our results with those from previous theoretical investigations. Our results confirm the oscillatory structures observed in the spin-averaged H(2s) and H(2p) excitation cross sections for impact energies below 50 keV/u. Furthermore, we interpret these oscillations as the consequence of interferences between excitation to H(2s) and H(2p(0)) in both spin-singlet and spin-triplet symmetries, as well as between electron capture to He(1s2p P-1, |M-L| = 1) and excitation to H(2p(1)) in spin-singlet symmetry.

The processes of single-electron charge exchange, excitation, and ionization during proton impact on H(2 l ) are investigated. We employ two different theoretical methods that are suitable for different collision energy regions: the full quantum-mechanical molecular orbital close-coupling method for energies from 0.001 to 1 keV u ^−1 and the two-center atomic orbital close-coupling (TC-AOCC) method for energies between 0.3 and 100 keV u ^−1 . For charge exchange and excitation processes, the total and nl -resolved cross sections to the final reaction channels of H ( nl , n = 1–4) have been obtained over a broad energy region. Moreover, the ionization cross sections in the TC-AOCC calculation are also reported for both H(2 s ) and H(2 p ) initial target states. The present results are all compared with those from other sources when available. It is found that the magnitude and energy behavior of nl -resolved excitation cross sections for H ^+ –H(2 p ) collisions are significantly distinct from those of the H(2 s ) initial state in the entire energy range considered, particularly in the low-energy region. The energy behaviors of the nl -resolved charge exchange cross sections from the H(2 p ) initial state are similar to those from the H(2 s ) initial state, but their magnitudes are larger. The present accurate cross-section data are anticipated to provide insight into the research of astrophysics and controlled fusion plasmas.

Complicated many-body interactions between ions and surrounding particles exist in warm and hot dense plasmas. It will significantly alter the atomic structures and dynamic properties of the embedded ions. Recently, the atomic-state-dependent (ASD) screening model has been proposed and shown to be valid for investigating the screening effect in warm and hot dense plasmas over a wide range of electron densities and temperatures. By employing the ASD model, we investigate the photoionization process for the hydrogenlike carbon ion embedded in warm and hot dense plasmas with corresponding Coulomb coupling parameter ranges of 0.05 <= Gamma <= 1.16, where I' characterizes the ratio of the average potential to thermal energy. It is found that there are stronger plasma screening effects on the ionization energy and photoionization cross section due to the negative-energy electron distributions considered in the ASD model compared to those considering only free electrons. The present results from the ASD model show reasonable agreement with the classical Debye-H & uuml;ckel (DH) model in weakly coupled plasmas. However, significant deviations of the ionization energy and cross section between these two models are observed in moderately and strongly coupled plasmas, due to the approximate treatment of the plasma-electron density distribution of the DH model. In the region of low photoelectron energies, the positions of the shape resonance peaks of the cross sections obtained from the ASD model differ significantly from those of the DH model due to the different screening effects.

As one kind of ubiquitous collision system, O6+ + He deserves attentive study due to its theoretical significance in fundamental physics and applied value in fields like astrophysics or plasma physics. Specifically, in the case of the electron capture process, while a considerable number of measurements and calculations have focused on single electron capture, research is still inadequate on the double electron capture which contributes nearly 10% to the overall electron capture. In this work, a two-active-electron semiclassical asymptotic-state close-coupling method is used to calculate the total and l-resolved state-selective double electron capture cross sections of O6+ + He collisions in the energy range 0.5-100 keV/u, accompanied by experimental measurements in the energy range 2.63-37.5 keV/u with an uncertainty of 16%, in good consistency. These theoretical and experimental data can fill gaps in the database of double electron capture in O6+ + He collisions and provide insights for improving theoretical models in further research.

We investigate keV collisions between antiprotons and the rare-gas atoms neon and argon. We use a correlated approach in which the eight electrons from the L shell of neon and M shell of argon are active and up to two-electron processes are included, going thus beyond the approximate theoretical approaches used so far. Our results show that the electronic correlation plays a major role in the single- and double-ionization processes. Furthermore, we show that two-electron processes contribute significantly to the electronic stopping power. These results apply to both target atoms studied in this paper and we therefore conclude that a correlated approach is in general necessary to obtain accurate antiproton electronic stopping-power cross sections. Our paper paves the way to a better understanding and knowledge of antiproton collision physics.

We report an experimental and theoretical study of state-selective charge exchange processes in Ar8+ on He collisions at 1 and 3 keV/amu, benchmarking the fundamental electron capture dynamics under strong perturbations. The quantum-state selectivity has been experimentally resolved for one 1s electron of He capture into 4s, 4p, 4d + 4 f, and 5s states of Ar7+ ion along with the corresponding scattering angle differential cross sections. By comparing to theoretical calculations with a two-active-electron semiclassical asymptotic-state close-coupling approach, we are able to verify the important role of electronic correlations during the collisions and that the impact parameter sensitive transition probability significantly mediates the state-selective specifics.

Research on electron capture (EC) process are undoubtedly helpful for maturing theoretical models on ion-induced collision especially for low-energy region. In this work, a two-active-electron semiclassical asymptotic-state close-coupling method was used to calculate the total and l -solved state-selective single EC cross sections of O 6+ + He collisions in the energy range of 0.3–100 keV u −1 , accompanied with experimental measurements in the energy range of 2.63–37.5 keV u −1 with an uncertainty of 11% in good agreement. Above 4.5 keV u −1 , the state-selective cross section of n = 5 was reported experimentally for the first time. Calculations with multiple theoretical methods were gathered and compared with present calculations. The importance of two-active-electrons correlation and large basis sets in theoretical calculations was found, and discrepancies between previous theoretical and experimental results can be explained by the present results.

Single- and double-electron capture (SEC and DEC) processes occurring in O ^6+ and H _2 collisions are investigated in a wide-energy domain ranging from 0.1 to 100 keV u ^−1 . Total and partial cross sections are calculated using a three-center, two-active-electron, semiclassical nonperturbative approach. To date, our close-coupling description of the collision is the most elaborate one in terms of accounting for electron correlation, molecular structures, and active channels. Our results are, in general, in good agreement with the available experimental ones for both total and partial cross sections. The comparison between the present calculations and available experimental data suggests that about 70% of the autoionization double capture may contribute to the measured SEC cross sections through postcollisional autoionization, while the stabilization of 30% of doubly excited states via the autotransfer to Rydberg states mechanism contributes to the measured DEC ones. Furthermore, we extend the understanding of the electron-capture processes on this system to impact energies above 20 keV u ^−1 for which no data exists. Our work provides new data for these electronic processes, which will be helpful for modeling astrophysical X-ray emissions induced by charge exchange.

Aims. The total and n -, l -, and S -resolved single-electron-capture cross sections for the collisions of O 7+ with atomic hydrogen are studied in the energy region from 10 −3 eV u −1 −5keV u −1 . Methods. These state-selective cross sections were calculated by employing the full quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio multireference single- and double-excitation configuration interaction approach, with optimized atomic basis sets to accurately describe the highly excited states, was used to obtain the adiabatic potentials and the radial and rotational coupling matrix elements that are required in the QMOCC calculation. Results. Our results are compared with other available theoretical and experimental data. The n = 5 manifold is the dominant reaction channel for the chasrge-transfer process for this collision system over the entire energy range, and our results agree better with the experimental data than the other theoretical results in the energy region in which they overlap because we included the necessary highly excited states in the expansion basis set. These charge-exchange cross-section data are useful for understanding and modeling the X-ray emission in astrophysical environments.

Utilizing a simplified quantum model approach, the low-energy inelastic collision processes between yttrium atoms (ions) and hydrogen atoms have been studied. Rate coefficients corresponding to the mutual neutralization, ion-pair formation, excitation, and de-excitation processes for the above collision systems have been provided in the temperature range of 1000-10 000 K. Three ionic states and 73 covalent states are considered in calculations for the collisions of yttrium atoms with hydrogen atoms, which include six molecular symmetries and 4074 partial inelastic reaction processes. For the collisions of yttrium ions with hydrogen atoms, one ionic state and 116 covalent states are included, which are related to three molecular symmetries and 13 572 partial inelastic collision processes. It is found that the rate coefficients for the mutual neutralization process have a maximum at T = 6000 K, which is an order of magnitude higher than those of other processes. Notably, the positions of optimal windows for the collisions of yttrium atoms and ions with hydrogen atoms are found near electronic binding energy -2 eV (Y) and -4.4 eV (Y+), respectively. The scattering channels located in or near these optimal windows have intermediate-to-large rate coefficients (greater than 10(-12) cm(3) s(-1)). The reported data should be useful in the study of non-local thermodynamic equilibrium modelling.

Elastic scattering of electrons on a finite-temperature quantum screened potential is studied by using the partial wave decomposition of scattering wavefunction. The influence of plasma temperature on the total and l = 0, 1, and 2 partial wave cross sections is systematically analyzed in the present work. It is found that when the plasma density is fixed, the screened strength does not change monotonically with temperature, which leads to different conditions for forming shape resonance in the scattering cross sections for the different temperature domains. The scattering cross sections under the environments of low temperature limit are compared with those for zero-temperature quantum plasmas.

The total, state-selective, and angular-differential cross sections for He2++H collision system in warm dense plasmas are studied by using the two-center atomic orbital close-coupling method in the energy range 0.1–300 keV/u. The calculations are performed for plasma density and temperature ranges ne ∼1018 to ∼1021 cm−3, Te = 0.3 eV–1.2 eV, typical for the H- and He-rich white dwarfs. The plasma environments are described by a unified screened potential involving electron degeneracy, finite-temperature gradient, and exchange-correlation effects. The results for H++H cases with the same plasma parameters are also presented for comparison to elucidate the discrepancies of plasma screening effects on the electron capture dynamics for collision systems with different nuclear symmetries. Moreover, classical Debye screening results are also given for comparison to clarify the effects of quantum correlations in warm dense plasmas on the electron capture dynamics. The present work is expected to provide theoretical and data support for the astrophysical plasmas.

Relativistic photoionization processes of an exemplary highly charged H-like ion Ar17+ for 1s1/2, 2lj (l = 0, 1), and 3lj (l = 1, 2) initial states are studied in plasmas with coulomb coupling parameter 0.007 < Γ < 0.202. Photoionization cross sections for both the strongly and weakly screened cases exhibit specific properties when their plasma densities and temperatures in the vicinities of the critical values at which nlj bound states enter the continuum. The electron degeneracy, finite-temperature gradient corrections, and quantum exchange-correlations effects have been included in the interaction between charged particles by the screened potential used in the present work. It is found that these effects for the plasmas with different coupled strength are reflected in the resonant regions of photoionization cross sections by comparing with Debye cases. The present work is expected to provide theoretical and data support for the fusion plasmas.

Single-and double-electron-capture processes occurring in Ar8+ and He collisions are investigated in a broad energy domain ranging from 0.1 to 100 keV/u. Total and partial cross sections are calculated using a two-active-electron semiclassical asymptotic-state close-coupling approach. For single-electron-capture cross sections the present results show the best overall agreement with available experimental data for both total and partial cross sections, and possible reasons for observed discrepancies are discussed. Furthermore, we extend the understanding of the electron-capture processes on that system to impact energies above 20 keV/u for which no data exist. The cross sections for double-electron-capture processes are also reported and show severe discrepancies with the rare available experimental data.

Total and subshell-selective charge exchange cross sections and the corresponding reaction rate coefficients for Neq+-H (q = 6-10) collision systems are calculated by utilizing the two-center atomic orbital close-coupling (TC-AOCC) method at impact energy between 0.1 keV/u and 500 keV/u. Good agreements with the experimental and other theoretical results are found for the total charge transfer cross section in the considered energy range and for those of the dominant charge-exchange channels for the higher collision energies. These charge exchange cross section data are useful for understanding and modeling the X-ray emission in environments where charge transfer is an important mechanism generating this emission. (c) 2021 Published by Elsevier Inc.

Charge transfer processes between weakly bound entities play an important role in various chemical and biological environments. In this combined experimental and theoretical work, we investigate the nature of charge-transfer processes in homogeneous atomic and heterogeneous atomic-molecular clusters. Our results reveal fundamentally different processes to be at play in pure argon clusters compared to mixed argon-nitrogen systems: We demonstrate that the former species decay via photon-mediated charge transfer while a nonradiative direct process is found dominant in the atomic-molecular cases. Our results are of general interest for studies on charge redistribution in more complex and biologically relevant samples where molecules are involved.

Single- and double-electron-capture processes occurring in the system of hydrogen ions colliding with alkaline-earth atoms, H+ + Mg, are investigated in a broad energy domain ranging from 0.25 to 180 keV. Total and state-selective cross sections are calculated using a two-active-electron semiclassical asymptotic-state close-coupling approach. Our results show the best overall agreement with experimental data, and possible reasons for observed discrepancies are discussed. Comparison of our cross sections with previous theoretical results further demonstrates the importance of electronic correlations between the magnesium valence electrons and the strong couplings between various important channels. Furthermore, our investigations suggest that the oscillatory structures observed in the double-electron-capture cross sections stem from complex coherence effects between double-electron capture, electron transfer to excited states, and transfer-excitation processes.

A combined experimental and theoretical study on single capture in 15-50 keV/uC(4+1) + He collisions was performed. State-selective single-electron capture cross sections and projectile scattering angle distributions were obtained by using a reaction microscope. A comparison of the state-selective cross sections with theoretical calculations based on the two-active-electron semiclassical atomic-orbital close-coupling method showed an excellent agreement for the considered impact energies. For the angular differential cross sections, an overall agreement was also obtained between the present experimental and theoretical results. Simulations performed using an extended Fraunhofer-type diffraction model suggest that the undulatory structures observed at small scattering angles for capture to C3+(1s(2)2s) and C3+(1s(2)2p(0)) can be interpreted as the diffraction pattern of the incident projectile de Broglie wave confined by an aperture defined as the region around the target where the considered capture process is likely. The strong competition between single-electron capture to C3+(1s(2)2p(0)) and C3+(1s(2)2p(1)) is also discussed to interpret the differences observed between their respective differential cross sections.

We present a simple and efficient method for computing single and double ionization cross sections in ion-atom and ion-molecule collisions using L-2 Gaussian basis sets. Gaussian functions are widely employed to compute bound states of ions, atoms, and molecules. However, the description of continuum states, and therefore ionization phenomena, remains a theoretical challenge. Our approach is tested on the benchmark system antiproton-helium collisions in the so-called intermediate energy range. A good agreement with numerically exact calculations is observed. The proposed method is general and can thus be employed in any collisional systems in the challenging nonperturbative regime. Our work opens the way to investigate multiple ionization processes by ion impact in multicenter polyelectronic systems.