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An ion embedded in warm/hot dense plasmas will greatly alter its microscopic structure and dynamics, as well as the macroscopic radiation transport properties of the plasmas, due to complicated many-body interactions with surrounding particles. Accurate theoretically modeling of such kind of quantum many-body interactions is essential but very challenging. In this work, we propose an atomic-state-dependent screening model for treating the plasmas with a wide range of temperatures and densities, in which the contributions of three-body recombination processes are included. We show that the electron distributions around an ion are strongly correlated with the ionic state studied due to the contributions of three-body recombination processes. The feasibility and validation of the proposed model are demonstrated by reproducing the experimental result of the line-shift of hot-dense plasmas as well as the classical molecular dynamic simulations of moderately coupled ultra-cold neutral plasmas. Our work opens a promising way to treat the screening effect of hot and warm dense plasma, which is a bottleneck of those extensive studies in high-energy-density physics, such as atomic processes in plasma, plasma spectra and radiation transport properties, among others. Atoms embedded in dense hot plasmas are affected by complex many-body interactions which challenges our capacity to model high energy density plasma. The authors propose a solution to the effects of many-body interactions on ions in dense plasmas, with a particular focus on the threebody interaction.

We study charge transfer of a multi-electron collision system Li2+ + Ar using the time-dependent density functional theory non-adiabatically coupled to the molecular dynamics. By implementing the particle number projection method, the single- and double-charge transfer cross sections are extracted at MeV energies, which are in good agreement with the experimental data available. The analysis of charge transfer probabilities shows that for energies higher than 1.0 MeV, the single-charge transfer occurs for a broader range of impact parameters, while the double-charge transfer is dominated by close collisions. To gain the population of captured electrons on the projectile, we compute the orbital projection probabilities. It is found that the electrons of the Ar atom will most possibly transfer to the 2p orbitals of the Li2+, and only a small portion of captured electrons distribute on the s orbitals. This work verifies the capability of the present methodology in dealing with charge transfer in dressed ion collisions at MeV energies.

The electron excitation processes of H(1s) + He(1s2) → H(2s/2p) + He(1s2) are studied in impact energy range of 20--2000 eV/u by using the quantum-mechanical molecular orbital close-coupling (QMOCC) method. Total and state-selective cross sections have been obtained and compared with the available theoretical and experimental results. The results agree well with available measurements in the overlapping energy regions overall. The comparison of our results with other theoretical calculations further demonstrates the importance of considering a sufficient number of channels. The datasets presented in this paper, including the excitation cross sections, are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00083.

The single, double, triple, and quadruple Auger decays of ${\mathrm{Ar}}^{+}(2{s}^{\ensuremath{-}1})$ are studied, based on many-body perturbation theory. The level-to-level investigation indicates that the double Auger primarily comes from the cascade process involving the Coster-Kronig decay. Moreover, the complex triple Auger and quadruple Auger decay are expressed by the multistep approach, i.e., the combination of cascade and direct processes. On the other hand, by employing the separate orbital sets for optimizing the single-electron wave functions, our ion yield ratios (${\mathrm{Ar}}^{2+}:{\mathrm{Ar}}^{3+}:{\mathrm{Ar}}^{4+}:{\mathrm{Ar}}^{5+}=3.5:88.7:7.5:0.26$) agree quite well with the recent experimental data (3:89:8:0.3) [Lablanquie et al., Phys. Chem. Chem. Phys. 13, 18355 (2011)]. Moreover, the single, double, and triple Auger spectra, as well as lifetime, are all in accord with the measurements of Lablanquie et al.

A contour deformation method (CDM) in the complex momentum plane has been successfully extended and implemented to probe resonances in atomic and molecular systems. Specifically, solution of the Schrodinger equation is performed in momentum space with momentum deformed on a contour in the complex plane. The bound, resonant, and complex continuum states could be directly revealed from the eigenvalues of the Schrodinger equation in the complex momentum plane. The calculations of shape resonances in electron scattering with Na+ in Debye plasmas (one channel), and in the charge transfer process H − ( 1 s 2 ) + Li ( 1 s 2 2 s ) ( 1 2 Σ + ) → H ( 1 s ) + Li − ( 1 s 2 2 s 2 ) ( 2 2 Σ + ) (coupled channels) are given as illustrative examples. It is shown that calculated results from CDM agree very well with those extracted from the eigenphase sum of scattering theories. The effectiveness of CDM is also demonstrated by comparing its results with those obtained by the complex rotation scaling and exterior complex scaling methods. The convergence of CDM results can be obtained by increasing the momentum integration region and the number of integration points. The studied examples demonstrate that CDM could be a powerful tool for studies of resonances in complex atomic and molecular systems.

Debye-screening effects on the electron-impact excitation (EIE) processes for the dipole-allowed transition 1s2 1 S → 1s2p 1P in He-like Al11+ and Fe24+ ions are investigated using the fully relativistic distorted-wave methods with the Debye–Hückel (DH) model potential. Debye-screening effects on the continuum-bound (CB) interaction and target ion are discussed, both of which result in reduction of EIE cross sections. This reduction due to screening on the CB interaction is dominant. The non-spherical and spherical DH potentials are adopted for considering the screening effect on the CB interaction. It is found that the spherical DH potential could significantly overestimate the influence of plasma screening on EIE cross sections for multielectron He-like ions.

The single- and double-electron capture (SEC, DEC) processes of He2+ ions colliding with Ne atoms are studied by utilizing the full quantum-mechanical molecular-orbital close-coupling method. Total and state-selective SEC and DEC cross sections are presented in the energy region of 2 eV/u to 20 keV/u. Results show that the dominant reaction channel is Ne+(2s2p 6 2 S) + He+(1s) in the considered energy region due to strong couplings with the initial state Ne(2s 22p 6 1 S) + He2+ around the internuclear distance of 4.6 a.u. In our calculations, the SEC cross sections decrease initially and then increase whereby, the minimum point is around 0.38 keV/u with the increase of collision energies. After considering the effects of the electron translation factor (ETF), the SEC cross sections are increased by 15%–25% nearby the energy region of keV/u and agree better with the available results. The DEC cross sections are smaller than those of SEC because of the larger energy gaps and no strong couplings with the initial state. Due to the Demkov-type couplings between DEC channel Ne2+(2s22p 4 1 S) + He(1s 2) and the dominating SEC channel Ne+(2s2p 6 2 S) + He+(1s), the DEC cross sections increase with increasing impact energies. Good consistency can also be found between the present DEC and the experimental measurements in the overlapping energy region.

The transition energies, E1 transitional oscillator strengths of the spin-allowed as well as the spin-forbidden and the corresponding transition rates, and complete M1, E2, M2 forbidden transition rates for 1s 2, 1s2s, and 1s2p states of He I, are investigated using the multi-configuration Dirac–Hartree–Fock method. In the subsequent relativistic configuration interaction computations, the Breit interaction and the QED effect are considered as perturbation, separately. Our transition energies, oscillator strengths, and transition rates are in good agreement with the experimental and other theoretical results. As a result, the QED effect is not important for helium atoms, however, the effect of the Breit interaction plays a significant role in the transition energies, the oscillator strengths and transition rates.

The electron-impact double ionization (DI) and triple ionization (TI) for O ii-iv ions are investigated using multistep approaches within the framework of many-body perturbation theory. The indirect DI and TI are treated as the single ionization of an inner-shell $1s$ electron followed by the single and double Auger decays, respectively. The knockout mechanism is employed to deal with the direct ionization process. The present approaches reproduce the available experimental cross sections for the DI of O ii-iv ions with much better accuracy compared to previous calculations. The TI cross sections of the O ii ion are calculated, which are in good agreement with the recent experimental data [Lecointre et al., J. Phys. B 46, 205201 (2013)]. It is found that the electron correlation effect and the energy distribution of the intermediate electron, which is taken as the incident electron of the subsequent knockout process, play an important role in the multistep treatment of the multiple ionization process.

The multi-electron capture and loss cross-sections of Ar+–Ne collisions are calculated at absolute energies in the few-keV/a.u. regime. The calculations are performed using a novel inverse collision framework, in the context of a time-dependent density functional theory, combined with molecular dynamics. The extraction of the capture and loss probabilities is based on the particle-number projection technique, originating from nuclear physics, but validly extended to represent many-electron systems. Good agreement between experimental and theoretical data is found, which clearly reveals the non-negligible post-collision decay of the projectile’s electrons, providing further evidence for the applicability of the approach to complex many-electron collision systems.

The Auger decay for the many-electron Xe+ (4 p 3 / 2 − 1 ) state is studied in detail, using multistep approaches. It is found that the single Auger decay channels are primarily Coster–Kronig processes, which is in accord with other theoretical and experimental results. The double and triple Auger decays result primarily from cascade processes, i.e., the sequential two-step and three-step Auger decay, and as such, the contributions from direct processes can be neglected. Level-to-level rates for single, double, and triple decays are obtained, based on which comprehensive Auger electron spectra and ion yields are obtained. Our decay paths and Auger electron spectra are in agreement with the experimental analysis [Hikosaka et al., Phys. Rev. A 76 (2007) 032708], and our ion yield ratios (Xe2+: Xe3+: Xe4+ = 4.6 : 87.0 : 8.4) are also in line with their values (5.0 : 86.0 : 9.0). However, with respect to the ion yield ratios, a discrepancy still remains among the experimental and theoretical results. Taking into account the complexity of Xe’s electronic structure, further, more detailed experiments are still required.

In molecules, the nonadiabatic couplings between two adiabatic potentials build the avoided crossing (AC) region. The rovibronic resonances in the AC region of two-coupled potentials are very special, since they are not in the bound state region of the adiabatic potentials, and they usually do not play important roles on the scatterings and are less discussed. Exemplified in particle scattering, resonances in the AC region are comprehensively investigated. The effects of resonances in the AC region on the scattering cross sections strongly depend on the nonadiabatic couplings of the system, it can be very significant as sharp peaks, or inconspicuous buried in the background. More importantly, it shows a simple quantity proposed by Zhu and Nakamura (1992 J. Chem. Phys. 97 8497) to classify the coupling strength of nonadiabatic interactions, can be well applied to quantitatively estimate the importance of resonances in the AC region. Example applications of the quantity for real molecules (MgH, CO and OH) can well explain the evolutions of cross sections in the AC region published in the literatures. This work provides a simple and practical way to determine the candidate molecules when studying the resonances in the AC region.

Theoretical studies of photodissociation cross sections of the beryllium monohydride cation BeH + are reported. Explicit photodissociation cross sections are computed for transitions from its ground electronic state X 1 Σ + to excited ones A 1 Σ + , B1Π and C 1 Σ + respectively. Partial cross sections are computed for nearly the full range of rovibrational levels of the X 1 Σ + state and for photon wavelengths ranging from 70 nm to threshold. Photodissociation cross sections are presented at temperatures of 1800 K, 4500 K, 10000 K and 20000 K as examples, where a Boltzmann distribution of initial rovibrational levels is assumed. This paper provides the complementary photodissociation cross sections following the bound-bound transition of previous work for BeH + [7] . The results are applicable to the photodissociation of BeH + in the early universe and in a variety of ultraviolet (UV) irradiated interstellar environments, which is of great importance to the modelling of features of interstellar observations as well as the fusion plasma emissions in the edge and divertor region.

The nonradiative charge-transfer processes of Be3+(1s)/B4+(1s) colliding with He(1s2) are investigated by the quantum-mechanical molecular orbital close-coupling (QMOCC) method from 10 eV/u to 1800 eV/u. Total and state-selective cross sections are obtained and compared with other results available. Although the incident ions have the same number of electrons and collide with the same target, their cross sections are different due to the differences in molecular structure. For Be3+(1s) + He(1s2), only single-electron-capture (SEC) states are important and the total cross sections have a broad maximum around E = 150 eV/u. While for B4+(1s) + He(1s2), both the SEC and double-electron-capture (DEC) processes are important, and the total SEC and DEC cross sections decrease rapidly with the energy decreasing.

We investigate the electron capture processes of N4+(1s 22s) colliding with He(1s 2) in the energy range of 10–1700 eV/amu using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. Total and state-selective single-electron capture and double-electron capture (SEC and DEC) cross sections are obtained and compared with other available studies. The results agree better with the experimental data in both trend and magnitude when the electron translation factor (ETF) effects are included. Our results indicate that both the SEC and DEC processes play important roles in the considered energy region. For the SEC processes, the N3+(1s 22p 2) + He+(1s) states are the dominant capture states, and the N2+(1s 22s2p 2) + He2+ states are the main DEC states.

The KLL dielectronic recombination (DR) process of C5+ ion embedded in Debye plasmas is investigated using the multiconfiguration Dirac-Fock method with the Debye-Huckel model potential. The resonance energies, radiative and Auger rates as well as DR cross sections are obtained for a large range of Debye screening parameters to explore the influences of the plasma screening on the KLL DR process of C5+ ion. It is found that the total radiative rates and Auger rates of the intermediate states both decrease monotonically with increasing the plasma screening, except the Auger rate for the transition 2p2 1S → 1s that changes nonmonotonically due to such screening imposed on the interaction between the configurations 1s and 2s in C5+ ion. Moreover, for the KLL DR process, blueshift and redshift phenomena are observed for the resonance energies, which originates from the dynamic variations of the energy levels of C4+ and C5+ ions in the Debye plasma. The magnitudes of the DR cross section decrease slightly when the Debye-screening effects are not so strong.

The multiple Auger decays of the $\mathrm{Ne}\phantom{\rule{0.28em}{0ex}}1{s}^{\ensuremath{-}1}$ state including double and triple Auger processes are investigated within the framework of perturbation theory. The contributions of the cascade and direct processes are determined for the double Auger decay. In the cascade processes, the choice of the orbital sets and configuration interaction can strongly affect the partial probabilities for the specific configurations of $\mathrm{N}{\mathrm{e}}^{3+}$. The multistep approaches, i.e., the knockout and shakeoff mechanisms, are implemented to deal with the direct double Auger processes for which the total and partial probabilities corresponding to specific configurations of $\mathrm{N}{\mathrm{e}}^{3+}$ are calculated and reveal that the knockout is dominant. Finally, the probabilities of the triple Auger decays that are decomposed into a double Auger process and a subsequent emission of a single electron are obtained using the cascade and knockout mechanisms. The calculated probabilities agree reasonably well with the available experimental data.

The calculation of triple-differential cross sections for the electron-impact ionization of $10{a}^{\ensuremath{'}}$ and $2{a}^{\ensuremath{'}\ensuremath{'}}$ orbitals of the formic acid (HCOOH) molecule has been carried out by the multicenter distorted-wave method. The coplanar asymmetric kinematics is considered at incident energies of 100 and $250\phantom{\rule{0.16em}{0ex}}\text{eV}$, where previous experiments and theories are available for comparison. The present calculations reproduce the experimental measurements satisfactorily and the results suggest that the nuclear distribution has important contributions on the cross sections at large momentum transfers.

The hyperfine induced $4f^{14}5s5p~^3\mathrm{P}^o_{0,2}~-~4f^{14}5s^2~^1\mathrm{S}_0$ transition probabilities for highly charged Sm-like ions are calculated in the framework of the multi-configuration Dirac-Hartree-Fock method. Electron correlation, the Breit interaction and quantum electrodynamical (QED) effects are taken into account. For ions ranging from $Z=79$ to $Z=94$, $4f^{14}5s5p~^3\mathrm{P}^o_{0}$ is the first excited state, and the hyperfine induced transition is an dominant decay channel. For the $4f^{14}5s5p~^3\mathrm{P}^o_{2}$ state, the hyperfine induced transition (HIT) rates of Sm-like ions with $Z=82-94$ are reported as well as the magnetic dipole (M1) $^3\mathrm{P}^o_2 ~-~ ^3\mathrm{P}^o_1$, the electric quadrupole (E2) $^3\mathrm{P}^o_2 ~-~ ^3\mathrm{P}^o_{0,1}$, and the magnetic quadrupole (M2) $^3\mathrm{P}^o_2 ~-~ ^1\mathrm{S}_0$ transition probabilities. It is found that M1 transition from the $4f^{14}5s5p~^3\mathrm{P}^o_2$ state is the most important decay channel in this range on $Z \ge 82$.

A numerical method based on Zabaydullin and Dubau's work [O. Zabaydullin and J. Dubau, J. Phys. B: At. Mol. Opt. Phys. 45, 115002 (2012)] has been developed to calculate the Cauchy principal value integral in scattering matrices and obtain photorecombination (PR) cross sections of low-lying resonances according to Davies and Seaton's theory [J. Phys. B 2, 757 (1969)], in which radiation damping is included. The Dirac $R$-matrix method is employed to secure the dipole matrix. Using this method, PR cross sections of ${\mathrm{C}}^{4+}$ for the KLL resonance are acquired, and compared with available experimental measurements and other close-coupling theoretical results. It is shown that our damped cross sections reproduce the experimental data and are in agreement with other theoretical results. Meanwhile, radiation damping can reduce the PR cross section for the $1s2{p}^{2}\phantom{\rule{4pt}{0ex}}^{2}P$ resonance (corresponding to two levels ${[{(1s2{p}_{1/2})}_{1}2{p}_{3/2}]}_{1/2}$ and ${[1s{(2{p}_{3/2}^{2})}_{2}]}_{3/2}$ by three orders of magnitude. The unresolved and underestimated resonances $1s2{p}^{2}\phantom{\rule{4pt}{0ex}}^{4}P, 1s2s2p\phantom{\rule{4pt}{0ex}}^{4}P$, and $1s2{p}^{2}\phantom{\rule{4pt}{0ex}}^{2}P$ in the undamped Breit-Pauli $R$-matrix calculations [H. L. Zhang et al., J. Phys. B: At. Mol. Opt. Phys. 32, 1459 (1999)] are corrected. Besides, dielectronic recombination cross sections of ${\mathrm{C}}^{4+}$ for the KLL resonance are also presented for comparison using the relativistic configuration-interaction (RCI) method implemented in flexible atomic code (fac), which show radiation damping has pronounced influences on $1s2{p}^{2}\phantom{\rule{4pt}{0ex}}^{2}P$ due to much larger radiative rates compared with autoionization rates. Furthermore, radiative and autoionization rates for the intermediate states ${[{(1s2{p}_{1/2})}_{1}2{p}_{3/2}]}_{1/2}$ and ${[1s{(2{p}_{3/2}^{2})}_{2}]}_{3/2}$ of the He-like ions with $6\ensuremath{\le}\phantom{\rule{4pt}{0ex}}Z\ensuremath{\le}83$ are calculated using fac, scaling laws of which are checked. Autoionization rates comply with the ${Z}_{\mathrm{eff}}^{0}$ scaling law for $Z\ensuremath{\ge}32$, which is caused by relativistic effects.

The nonradiative single-electron-capture (SEC) processes for N5+(1s2) colliding with He atoms are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. Total and state-selective SEC cross sections are obtained in the energy range of 3 – 1700 eV/amu, for which the ab initio potential curves and nonadiabatic coupling matrix elements (involving physical and pseudo states) are computed by using the multireference single- and double-excitation configuration-interaction (MRD-CI) method. It is found that the pseudo states are also important to obtain the convergent results, especially in the low energy region. Moreover, our results indicate that the n = 3 states are the dominate states in the considered energy region, and that the electron translation factor effects (ETF effects) become important when the energy is above 1 keV/amu. In addition, it is observed that the total and state-selective cross sections for SEC are in general agreement with all available experimental data.

The n-, (n,l)- and fine-structure level state-selective radiative recombinations (RR) cross sections of argon ions Ar18+,Ar13+,Ar7+ and Ar+ are obtained with the semi-classical Kramer formula, the relativistic self-consistent field (RSCF) method and the relativistic configuration interaction (RCI) method. It is found that for the highly charged ions with few electrons, the cross sections calculated with these three methods are in good agreement with each other. But as the number of electrons increases, the Kramer formula deviates from the RSCF and RCI results. For instance, when the energy of the incident electron is larger than 100 eV, the n-state selective cross sections of Ar7+ calculated from the Kramer formula are underestimated for more than 50%. The RSCF results are in general agreement with the RCI results. However, for the low charged ions, a clear distinction appears due to the strong configuration interaction, especially near the Cooper minimum. The n-resolved (n≤10) and total Maxwellian averaged rate coefficients are calculated, and the analytic fitting parameters are also provided.

Single, double, and triple Auger decay rates of ${\mathrm{C}}^{+}(1s2{s}^{2}2{p}^{2}{\phantom{\rule{0.16em}{0ex}}}^{2}D,{\phantom{\rule{0.16em}{0ex}}}^{2}P)$ resonances were calculated in the framework of perturbation theory. The direct double Auger decay probabilities were calculated by using the approximate formulas according to the knockout and shakeoff mechanisms, in which the knockout mechanism was found to be dominant. Then the knockout mechanism was employed to investigate the complex triple Auger decay process, and the calculated rates have good agreement with the available experimental values.

The multiconfiguration Dirac-Hartree-Fock method was employed to calculate the total and excitation energies, oscillator strengths, and hyperfine structure constants for low-lying levels of Sm i. In the first-order perturbation approximation, we systematically analyzed correlation effects from individual electrons and electron pairs. It was found that the core correlations are of importance for the physical quantities concerned. Based on the analysis, the important configuration state wave functions were selected to constitute atomic state wave functions. By using this computational model, our excitation energies, oscillator strengths, and hyperfine structure constants are in better agreement with experimental values than earlier theoretical works.

We present a theoretical study of relativistic effects on the linear polarization and angular distribution of x-ray radiation for the L () characteristic line following inner-shell single photoionization of Cd, Ba, Yb and Ra atoms. The analysis is performed based on the multi-configuration Dirac–Fock method and the density matrix theory. To explore the nature of these effects, calculations are carried out based on detailed analyses of the total and magnetic sublevel cross sections, the linear polarization, and the angular distribution of the x-ray photoemission, as well as on corresponding data calculated in the nonrelativistic limit. Our results show a significant difference in the above parameters compared to the nonrelativistic treatment, which is mainly due to the relativistic treatment of the target. Higher multipole contributions are also estimated, and found to be generally weaker. The importance of inclusion of the relativistic effects grows with increasing atomic number and the incoming photon energy.

The dielectronic recombination (DR) of neonlike gold ions is investigated employing the flexible atomic code based on the relativistic configuration interaction method, and its influence on the ionization balance and radiation energy in high-temperature plasma is also studied. The total resonance strength for LMM configuration complex is in a good agreement with the experimental measurement and other theoretical works. The DR rate coefficients are calculated and compared with the three-body recombination and radiative recombination rate coefficients. The DR process is the dominant recombination mechanism of Ne-like gold ions for plasma with temperature Te≥6.5 keV and density ne≤2×1022 cm-3, which is close to the condition of X-ray conversion region in the inertial confinement fusion. Moreover, the DR satellite spectra of LMM, LMN and LMO resonances are simulated, and compared with the intensities of the corresponding resonance lines induced by the electron impact excitation. The intensity ratio of the satellite line 3D’ $[(2p^{5}_{3/2}3d_{3/2}3d_{5/2})_{J=5/2}$ – $(2p^{6}3d_{3/2})_{ J=3/2}]$ and the resonance line 3D $[(2p^{5}_{3/2}3d_{5/2})_{J=1}$ – $(2p^{6})_{J=0}]$ is given, which can be applied for diagnostics of plasma temperature.

A multicenter distorted-wave (MCDW) method for fast-electron-impact single ionization of a molecular system in the coplanar-asymmetric kinematics is developed. Plane waves are used to describe the fast incoming and outgoing electrons and the multicenter nature of the molecule is considered by describing the slow ejected electron with the multicenter distorted wave, which is solved from the anisotropic multicenter potential between the ejected electron and the ionic molecule. The MCDW method improves the conventional molecular distorted-wave methods, whose distorted wave is solved from the spherically averaged isotropic potential. The application to the water molecule shows reasonable agreement with the available experimental data.

Using the fully quantum-mechanical approach, the radiative charge transfer for H + + Na(3s) collisions has been investigated. The charge transfer emission spectra are analyzed at resonant and non-resonant collision energies. The radiative association cross sections, obtained by subtracting the radiative charge transfer part from total radiative decay cross sections calculated by the optical potential method, are presented in the energy range 10 −6 –1 eV.

Photoion and photoelectron data for hollow lithium states were recently reported with increased spectral resolution. In order to reproduce and identify the important resonances due to ${2ln}^{\ensuremath{'}}{l}^{\ensuremath{'}}{n}^{\ensuremath{''}}{l}^{\ensuremath{''}}$ ${}^{2}{P}^{o}$ autoionizing states new photoionization calculations have been performed using the R-matrix code with a 29-term target representation for incident photon energies between 140 and 167 eV. Excellent agreement between theoretical and measured results over partial or total photoionization cross sections confirms the quality of the theoretical model. A determination of the resonance positions for each series converging to a ${2l2l}^{\ensuremath{'}}$ ${}^{1,3}L$ threshold of Li is proposed.

A simplified relativistic configuration interaction method is used to calculate the dielectronic recombination cross sections and rate coefficients for heliumlike carbon. In this method, the infinite resonant doubly excited states can be treated conveniently in the frame of Quantum Defect Theory. Our calculated cross sections are in agreements with the experimental measurements except for the 1s2lnl'(n=6,7) resonances. The total energy-integrated cross sections and rate coefficients over all dielectronic resonances are in agreements with the experimental measurements within percent.

Calculations of 1s electron inner-shell photoionization from the 1s(2)2s S-2(e) Li ground state have been performed using recent developments of the R-matrix code with a 19-term target representation for incident photon energies up to 130 eV. This photon energy range allows important resonances in the partial cross sections due to 1 snln'l' autoionizing states to be obtained. Theoretical resonant results are compared with recent experimental measurements of Kiernan et al, [J. Phys. B 29, L181 (1996)] in the 1s2l threshold region. Partial cross sections, branching ratios, and asymmetry parameters are also compared outside the resonant energy range with previous theoretical results of Lisini, Burke, and Hibbert [J. Phys. B 23, 3767 (1990)], who used the R-matrix code with an 11-term target representation, as well as the corresponding experimental result; of Ferret et al. [Phys. Rev. A 36, 3172 (1987)], Langer et al. [Phys. Rev. A 43, 1652 (1991)], and Cubaynes et al. (private communication). [S1050-2947(98)05702-3].

We have developed a simplified relativistic configuration-interaction method to calculate the dielectronic recombination (DR) cross sections and rate coefficients. In this method, the infinite resonant doubly excited states can be treated conveniently in the framework of quantum defect theory. Here we report a systematic study of DR rate coefficients of hydrogenlike isoelectronic sequence with atomic number 2 less than or equal to Z less than or equal to 79. The behavior of the DR rate coefficients along the isoelectronic sequence is studied. The results are compared with the Burgess formula and other theoretical works. Because of its relativistic treatment, our method can be applicable for arbitrary Z ions and the validity of the widely used Burgess formula can be examined, e.g., for the ion with Z greater than or equal to 36, the results calculated from Burgess formula would be larger by a factor of 2. [S1050-2947(98)01902-7].

Based on the R-matrix method, photoionization cross sections of He below the N = 2 threshold of He+ are calculated, and a definite assignment of the doubly excited resonance states is determined by the eigenchannel treatment. Our results are in good agreement with the experimental data and other theoretical works. The polarization effects on the doubly excited states are studied in detail. We elucidate the effects of the dynamic polarization within the reaction zone (i.e., R-matrix box) and the long-range static polarization potentials outside the reaction zone, which influence the resonance energies and the profiles of He resonance states. [S1050-2947(98)00802-6].

We here present an alternatve way to perform R-matrix calculations in which the eigenchannel parameters of multichannel quantum defect theory are calculated directly. Merits of our R-matrix calculations are twofold: (1) an analytical treatment of perturbed discrete Rydberg states, autoionizing states, and their adjacent continuum to avoid numerical calculations outside the R-matrix box; (2) clear assignment of overlapped resonances, e.g., to analyze the lithium inner-shell photoionization cross section, which has been of considerable interest in recent experimental measurements.

The nonradiative single-electron-capture (SEC) and double-electron-capture (DEC) processes for C${}^{4+}$(1${s}^{2}$) colliding with He atoms are investigated by using the quantum-mechanical molecular-orbital close-coupling method. Total and state-selective electron-capture cross sections are calculated in the energy range of 10${}^{\ensuremath{-}6}$--6 keV/amu. For energies less than 2 keV/amu, the DEC dominates the electron-capture processes. As the energy increases, the SEC cross sections increase while the DEC cross sections decrease; when $E$ g 2 keV/amu, the SEC process becomes the dominant mechanism. It is found that the SEC processes mainly result from the electron capture to $n$ = 3 channels of C${}^{3+}$ ion for energy below 0.7 keV/amu and from $n$ = 2 channels for $Eg0.7$ keV/amu. Compared with the available theoretical calculations, better agreement is achieved between the present results and the available measurements for total DEC and SEC cross sections. For state-resolved cross sections, excellent agreement is obtained for two-electron capture to C${}^{2+}$(2${s}^{2}$), C${}^{2+}$(2$s$2$p$), and C${}^{2+}$(2${p}^{2}$) and one-electron capture to C${}^{3+}$(2$s$) and C${}^{3+}$(2$p$) between the present calculations and the available theoretical and experimental results.

The nonradiative charge-transfer processes in Na${}^{+}$+${}^{87}$Rb(5$s$) collisions have been investigated by using the quantum-mechanical molecular-orbital close-coupling method and the two-center atomic-orbital close-coupling method for the energy range of 10${}^{\ensuremath{-}4}$--5 and 0.3--100 keV/u, respectively. The radiative charge-transfer, radiative-decay, and radiative-association processes have been investigated by using the fully quantum, optical-potential, and semiclassical methods for the energy range of 10${}^{\ensuremath{-}18}$--0.2 eV/u. The nonradiative charge-transfer processes dominate the collisions for energies above 0.2 eV/u and radiative-decay processes dominate in the lower-energy region. At the very low collision energies of 10${}^{\ensuremath{-}18}$--10${}^{\ensuremath{-}3}$ eV/u, the radiative-association process is more important than the radiative charge-transfer process. Most importantly, it is found that the radiative cross sections exhibit Langevin behavior as ${E}^{\ensuremath{-}1/2}$ for energies less than 10${}^{\ensuremath{-}2}$ eV/u.

The charge transfer processes for the Beq++H(q = 1-4) collisions are investigated by the quantum-mechanical and semiclassical methods in wide energy ranges. The total, n-selective, nl-selective, singlet and triplet charge transfer cross sections are obtained and compared with other available theoretical data. The total and n-selective data are presented. The validity of different methods is discussed. The recommend cross section data are given for all collision systems.

We here combine the eigenchannel theory and R-matrix theory to calculate the eigenchannel parameters of multichannel quantum defect theory directly. There are two advantages: (1) an analytical unified treatment of perturbed discrete Rydberg states, autoionizing states and their adjacent continuum to avoid numerical calculations outside the R-matrix box; (2) clear assignment of overlapped resonances.

Technical problems connected with use of the Born-Oppenheimer clamped-nuclei approximation to generate electronic wave functions, potential energy surfaces (PES), and associated properties are discussed. A computational procedure for adjusting the phases of the wave functions, as well as their order when potential crossings occur, is presented which is based on the calculation of overlaps between sets of molecular orbitals and configuration interaction eigenfunctions obtained at neighboring nuclear conformations. This approach has significant advantages for theoretical treatments describing atomic collisions and photo-dissociation processes by means of ab initio PES, electronic transition moments, and nonadiabatic radial and rotational coupling matrix elements. It ensures that the electronic wave functions are continuous over the entire range of nuclear conformations considered, thereby greatly simplifying the process of obtaining the above quantities from the results of single-point Born-Oppenheimer calculations. The overlap results are also used to define a diabatic transformation of the wave functions obtained for conical intersections that greatly simplifies the computation of off-diagonal matrix elements by eliminating the need for complex phase factors. © 2013 Wiley Periodicals, Inc.

Plasma screening effects on the energy structure and radiative transition properties of helium-like C4+ ions embedded in Debye plasmas are investigated by using the multi-configuration Dirac-Hartree-Fock method incorporating the Debye-Huckel potential for both the electron-nucleus and electron-electron interactions. Seventeen fine-structure energy levels of the low-lying 1s 2, 1s2l(l = s,p) and 1s3l′(l′ = s,p,d) configurations, as well as the electric-dipole (E1), magnetic-dipole (M1) and magnetic-quadrupole (M2) transition probabilities and oscillator strengths between these levels have been calculated over a wide range of screening parameters. It is found that the plasma screening leads to a decrease of excitation energies and alters the energy levels remarkably. For Δn ≠ 0 transitions, the spontaneous decay spectra are red-shifted and their oscillator strengths and transition probabilities decrease with increasing the interaction screening, while those for the Δn = 0 transitions exhibit opposite patterns. The influence of electron-nucleus and electron-electron screened interactions on the changes of energy levels and transition properties are analyzed. Comparison is made of present results with other data available in the literature for this ion.

The resonant charge transfer process for Li+–Li(2s) collision is investigated by the quantum-mechanical molecular orbital close-coupling(QMOCC) method and the two-center atomic-orbital close-coupling(AOCC) method in an energy range of 1.0 e V/u–104e V/u. Accurate molecular structure data and charge transfer cross sections are given. Both the allelectron model(AEM) and one-electron model(OEM) are used in the QMOCC calculations, and the discrepancies between the two models are analyzed. The OEM calculation can also give a reliable prediction of the cross sections for energies below 1 ke V/u.

We have performed fully relatively level-to-level distorted-wave (LLDW) calculations for both direct ionization (DI) and excitation autoionization (EA) of ground state Se3+ ion using the flexible atomic code (FAC). Large EA contributions come from the excitations 4p to nl and 3d to nl. Our calculated total DI+EA cross section have been compared with the recent experimental results. It suggests that the contributions of resonace-excitation double-autoionization process (REDA) to electron impact single ionization of Se3+ at the near threshold are more than 25%.