Momentum-space close coupling calculations of electron scattering require removal of spurious and unphysical solutions. We demonstrate here that removal of these solutions involve regulator operators that enforce Pauli exclusion selection rules in addition to removing spurious solutions. The form of a regular operator for e-H scattering has already been established, but a general extension to the multielectron case has been elusive. Here we present a general method for scattering on multielectron targets, atoms, or molecules, ensuring that the scattering solutions obey Pauli-exclusion selection rules. The regulator operator is obtained by finding the null space vectors of the N + 1 electrons of the projectile and target atom scattering system. We demonstrate that this general procedure reduces to the e-H result and provide examples for He- and Li-like targets as well as guidance for implementation.

Close-coupling calculations of electron-atom scattering yield excitation cross sections for atomic eigenstates of relatively small principal quantum number n << n(max )and orbital angular momentum l << l(max) included in the close-coupling expansion. We use the photoionization of the helium system to demonstrate that finite convergent close-coupling calculations can be used to estimate the excitation cross sections of the residual ion to arbitrarily high principal quantum number n>n(max )and orbital angular momentum l>l(max). In doing so, we demonstrate the utility of the step-function property of the positive-energy state cross sections, together with the negative-energy state cross sections, in determining the desired cross sections for arbitrarily high Rydberg states

Low-energy cosmic rays (E less than or similar to 1 GeV) are responsible for the ionization and heating of molecular clouds. While the role of supra-thermal electrons produced in the ionization process in inducing excitation of the ambient gas (mostly molecular hydrogen) has been studied in detail, the role of primary cosmic-ray nuclei (protons and heavier nuclei) has been generally neglected. Here, we introduce, for the first time, cross sections for proton impact on H2, calculated using the semiclassical implementation of the molecular convergent close-coupling method. Our findings show that proton-induced H2 excitation is comparable in magnitude to that caused by electrons. We discuss the possible implications on the estimate of the cosmic-ray ionization rate from observations in the near-infrared domain and on the cosmic-ray-induced H2 ultraviolet luminescence. We also derive a new approximated analytical parametrization of the spectrum of secondary electrons that can be easily incorporated in numerical codes.

The predictive capabilities of population models, such as collisional-radiative and corona models, for atomic and molecular hydrogen benefit from the recent advances in the availability of reaction probabilities, particularly due to the quantum mechanical convergent close-coupling (CCC) and molecular CCC (MCCC) methods. The CCC method provides, for the first time, an extensive set of cross sections for the electron impact excitation of atomic hydrogen that are accurate at the excitation threshold, thus enabling precise model predictions at low electron temperatures. The MCCC method provides consistent sets of cross sections for electron impact (de-)excitation of molecular hydrogen with different ro-vibrational resolution, thus enabling for the first time the development of a consistent set of population models with different detail level. This consistent set of population models allows investigations with different detail level of the plasma kinetics based on the same data basis. This work guides through the (differently resolved) population models based on the Yacora solver for atomic (Yacora H) and molecular hydrogen (Yacora H 2, Yacora H 2( X1, v), Yacora H 2( v), Yacora H 2( v, N) Fulcher) applying state-of-the-art reaction probabilities and demonstrates the respective individual application possibilities.

Theoretical spectral line shapes describe the distribution of opacity due to bound electronic transitions in hot dense plasmas and are used to fit emergent spectra from many astrophysical sources. Deficiencies in line broadening theory have been proposed as a possible explanation for unresolved discrepancies between theoretical and observed spectra in white dwarf star atmospheres and laboratory experiments at white dwarf star photosphere conditions. One possible source of these discrepancies is the formation of quasi-molecules. Quasi-molecules are close (unbound) collisions between atoms, which broaden line shapes and create additional satellite lines. Quasi-molecules are challenging to implement into traditional line shape codes and have historically required a number of physical approximations beyond what is used in standard Stark broadening models. Here we present a new approach to calculating line shapes with quasi-molecular resonances, using a novel multiple-basis method that considers both atomic and molecular states. We implement this approach into a simulation line shape code, present hydrogen Lyman-series line shapes with quasi-H_2^+ resonances, and demonstrate the impact our new line shapes have on hydrogen-atmosphere white dwarf star model spectra. We find that our new approach leads to broader quasi-molecular features that agree well with observed spectra in initial comparisons.

Effective tokamak disruption mitigation is crucial for ensuring the safety and integrity of fusion power reactors. Accurate collisional-radiative (CR) modeling of a radiative plasma is a critical component in predictive disruption mitigation design. In this paper, we focus on quasi-steady-state CR modeling applicable to the current quench phase of a tokamak disruption. We employ the ATOMIC collisional-radiative code from the Los Alamos suite and the newly developed Fusion Collisional-Radiative (FCR) code to model the atomic processes, providing high-fidelity data for radiative power loss, as well as average and effective charge states for hydrogen, helium, neon, and argon plasma species over a wide range of tokamak-relevant electron temperatures and electron densities. Fine-structure-resolved CR models are used for hydrogen and helium plasma species, while configuration-average CR models are implemented for neon and argon plasma species. The calculated values are compared with the superconfiguration CR model (FLYCHK) and the commonly used coronal equilibrium approximation to demonstrate the advantages and limitations of each model. To facilitate coupling of high-fidelity CR data to plasma simulation models, we represent the ATOMIC/FCR results over the relevant plasma parameter range using a smooth tensor product B-spline surface in electron temperature and electron density. This approach yields compact coefficient tables that can be evaluated efficiently while preserving spline smoothness across the domain. These data were previously used to examine ways to minimize runaway electrons in a tokamak current quench, and they are now made available in easy-to-use forms for community use and benchmarking.

In a combined experimental and theoretical study, M & uuml;ller et al. [Phys. Rev. A 111, 053108 (2025)] revealed highly detailed resonant structure in ionization with excitation and in double ionization of the Li-like B2+ ion. That work demonstrated the strong predictive power of the convergent-close-coupling (CCC) method when enhanced by modern supercomputing technology. In the present work, we apply CCC to analogous ionization processes in the Li atom. Again, we find K-shell ionization accompanied by K-shell excitation to contribute relatively strongly to the double photoionization of three-electron Li. Comprehensive detailed comparisons with the existing experimental data are presented and discussed.

The vibrational excitation of molecular hydrogen (H2) by low-energy electrons is one of the most fundamental reactions in atomic and molecular physics, playing a key role in the chemistry of the interstellar medium and studies of fusion plasmas. Crossed-beam experiments and electron swarm measurements have long been used to determine scattering cross sections for vibrational excitation, but the two methods produce conflicting results, a disagreement that has persisted for more than five decades and remains unsolved. Theoretical treatments have historically relied on approximations tailored to specific processes, such as separating the direct and resonant pathways or employing model polarization potentials, with no single method accurately describing all vibrational transitions. The absence of benchmark-quality calculations, combined with decades-long disagreements between experimental methods, means that even for this simple problem, there are no definitive cross-section data, leaving the reliability of theoretical approaches applied to more complex molecules uncertain and without quantified error bounds. Here we present ab initio calculations of low-energy vibrational excitation in H2 that treat electronic and vibrational motion on equal footing, providing a unified description of direct and resonant scattering across all vibrational transitions. The results are in stark contrast with previous theoretical estimates for many vibrational transitions, revealing systematic differences in both magnitude and energy dependence. At the same time, they provide strong confirmation of the swarm-derived cross sections, unlike previously accepted calculations that favored the beam data. This reversal of the long-standing situation shifts attention away from the swarm data and back onto the interpretation of the crossed-beam measurements. By providing accurate and self-consistent cross sections for vibrational excitation of H2, the present calculations will enable more reliable modeling of low-temperature plasmas and interstellar clouds.

A joint experimental and theoretical study is reported for inelastic backscattering of high-energy electrons from He. Electron energy loss spectra of He are measured, as a function of the azimuthal angle, at a scattering angle of 135 degrees and at an incident electron energy of 2 keV. It is shown that azimuthal angle dependencies observed for peak positions of the 11S-21S and 11S-21P inelastic bands as well as the 11S-11S elastic band certainly follow the law of conservation of energy regarding binary collision of electron projectile and scattering helium nucleus. Furthermore, the ratios of the two inelastic scattering cross sections to the elastic scattering are observed to be 1.82(12) & times; 10-3 and 1.55(11) & times; 10-3, respectively. It is also shown that the experimental cross section ratios are well reproduced by both second-order Born and convergent close-coupling calculations, while first-order Born calculations predict several orders of magnitude smaller values. In addition, an easy-to-understand scenario of the inelastic backscattering of high-energy electrons is discussed.

The relativistic convergent close-coupling method is applied to calculate cross sections for electron scattering on Ga+ ions. Integrated excitation cross sections are presented for the ground 3d(10)4s(2) 1S(0) electronic state for incident energies between the first excitation threshold and 500 eV. Rate coefficients for these transitions are presented assuming a Maxwellian electron energy distribution. Estimates are presented for the integrated single ionisation cross section (ISICS) for scattering on the 4s(2) S-1(0) and 4s4p P-3(j)degrees states for j is an element of{0,1,2}, including direct ionisation from the 4s, 4p and 3d electrons, and excitation autoionisation contributions from 3d electrons. Mixed agreement was found between the present ISICS and existing data.

Ji et al. [New J. Phys. 26, 093014 (2024)] established a direct link between the photoionization cross section and the attosecond time delay near Cooper minima (CM) in the valence shells of noble-gas atoms. This link is based on the analytic properties of the ionization amplitude in the complex plane of the photoelectron energy, and is particularly sensitive to the winding number of the amplitude around the origin of the complex energy plane. Here, we demonstrate an analogous relation for photoionization of the valence ns shells of alkali-metal atoms (AMA), from Na (n = 3) to Cs (n = 6), as well as alkaline-earth-metal atoms (AEMA), from Mg (n = 3) to Ba (n = 6). To this end, we employ a fully relativistic formalism that separates the two complementary ns1/2 -> Ep1/2 and Ep3/2 ionization channels. Each of these channels exhibits a phase variation close to pi, but in opposite directions, near their respective Cooper minima. This phase variation vanishes in a nonrelativistic formulation, where the two channels become degenerate. For AMA, due to the threshold proximity of the CM, the universal Coulomb contribution to the time delay must be subtracted. The remaining component of the time delay is target-specific, angular-dependent, and accessible through comparative measurements.

Cross sections for electron impact dissociative excitation and ionization in scattering on vibrationally excited levels of the ground electronic state of H_{3}^{+} and its isotopologues are reported in the energy range of 8 to 1000 eV. Calculations have been performed using a newly developed version of the molecular convergent close-coupling code. Cross sections for total dissociative excitation, ionization yielding atomic fragments such as D^{+}, and the total inelastic cross section are presented. Good agreement with available experiments has been demonstrated.

The molecular convergent close-coupling (MCCC) method is utilized to calculate cross sections for electron scattering on the ground state of Li2. A model-potential approach is used to represent Li2 as a quasi-two-electron system above a frozen core, and configuration-interaction calculations are performed to obtain the valence states. Cross sections are calculated at incident electron energies between 0.01 and 500 eV, for elastic, excitation, ionization, and total scattering. Comparison is made with previous results where available. For the elastic-scattering cross section, qualitative agreement is found with previous calculations at low incident energies, and quantitative agreement is found at higher energies. The previously predicted 2 Pi u shape resonance is also found in the present calculations, but at a substantially lower energy and with a larger magnitude. Mixed agreement is found with previous calculations for the excitation of the 1 1 Sigma u+ and 1 3 Sigma g+ states, and for ionization. The MCCC total cross section is in reasonable agreement with the only available experiment at incident energies greater than 0.5 eV.

The single-center convergent close-coupling method is utilized to calculate positron scattering from H-like ions from He+ to F8+. Results for the normalized annihilation rate ( Zeff) and the electron-loss, elastic, and bound-state excitation cross sections are obtained for energies up to 10 keV. Excellent agreement is found between present and previous theoretical Zeff results for He+, Li2+, B4+, and F8+. As there is no previous work for the remaining cross sections the results for electron-loss are presented alongside previous theory and experiment for incident electrons. The differences between these cross sections give an insight to the impact of the projectile charge on scattering from highly-charged ions.

We revisit the current status of high-precision calculations for electron-impact excitation of the (1s3s)3,1S states in helium in the low-energy near-threshold regime that is characterized by a large number of resonance features. Having noticed discrepancies between predictions from two previous large-scale calculations for this problem, we report new results and make recommendations regarding the absolute cross-sections that should be used in modeling applications.

EDGE2D-EIRENE profiles characteristic for low recycling, high recycling and detached plasmas are postprocessed applying a vibrationally resolved collisional radiative (CR) model based on the Yacora solver to predict excited state densities and thus the molecular Lyman-, Werner- and Fulcher band emission intensities. These emission intensities are compared to predictions from the AMJUEL database standardly used in EIRENE. Lower Fulcher band and higher Lyman- and Werner band emission is predicted by the Yacora model in comparison to AMJUEL suggesting that inconsistent results from model based evaluation of measured spectra are expected depending on which model and molecular emission band is considered. The implications on detachment rate predictions are discussed.

Cross sections for electron impact dissociative excitation and ionization in scattering on vibrationally excited levels of the ground electronic state of H3+, D3+, and T3+ are reported in the energy range of 8-1000 eV. Calculations have been performed using a newly developed version of the molecular convergent close-coupling code. Convergence of the cross sections with the size of the projectile partial-wave and close-coupling expansions is examined. Branching ratios and cross sections for the yields of D2+ and D+ from dissociative excitation of D3+ are presented and isotope effects are investigated. Cross sections for total dissociative ionization yielding atomic fragments such as D+ are presented and the total inelastic cross section is produced. Good agreement with available experiments has been demonstrated.

Single and double photoionization of the Li-like B2+(1s22s2S) ion were studied both experimentally and theoretically in the energy range from approximately 250-1200 eV. The cross section a23 for net single ionization in that range is dominated by direct removal of one K-shell electron, a process that is described very well by theory. Accordingly, measured yields of B3+ photoproducts were normalized to theory to obtain absolute cross sections a23. Aside from direct single ionization, there are additional contributions to a23 from photoabsorption resonances. The parameters of the Fano profile of the most prominent of these resonances, the triply excited 2s22p 2P state, were calculated by employing the convergent close coupling (CCC) approach and the theoretical results were experimentally verified. Using the normalization procedure obtained from the investigation of single ionization, also the measured yields of B4+ product ions could be put on an absolute cross-section scale. The resulting experimental cross section a24is in good accord with the CCC calculations revealing unexpectedly strong contributions that arise from ionization with excitation of B2+(1s22s2S) forming intermediate autoionizing B3+(nt n'I') levels, which subsequently decay to B4+ by Auger-electron emission. In addition, contributions to a24 from resonant excitation of B2+(nt n'I' n''I'') with n, n', n'' 2 could be identified. These triply excited resonances with an empty K shell can decay by simultaneous or sequential emission of two electrons and thus contribute to net double photoionization of the parent B2+ ion.