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During the last decades, the electron impact excitation (EIE) process has aroused much interest in various research areas. This process is crucial to the diagnoses of astrophysical and laboratory plasmas. Moreover, the EIE studies play an important role in understanding the quantum electrodynamic, many-electron, and hyperfine interaction effects in heavy atomic systems. As is well known, when ions are excited by collisions with a unidirectional beam of electrons, the magnetic sublevels of the excited state may be populated with nonstatistical probability. In the decay of the excited state, the emitted radiation is found to be anisotropic and polarized. From the analysis of the polarization, valuable information can be obtained. These properties have become indispensable tools for the diagnosis of plasma state and the analysis of complex spectrum formation mechanism. Up to now, however, most of studies have dealt with the linear polarization of X-ray radiation. Fewer publications have reported the circular polarization. Moreover, theoretical studies of the characteristic X-ray emission have just dealt with ions having zero nuclear spin, or have simply omitted all contributions that arise from such a spin. It is known that some kinds of ions each have a nuclear spin I 0. Owing to the hyperfine coupling, new decay channel will be open, namely, hyperfine-induced transition. It is thus important to analyze how the hyperfine interaction affects the polarization properties of X-ray radiation. In this study, we present a systematically theoretical analysis of the polarization and angular distribution of X-ray radiation during the hyperfine-induced transition. The calculations are performed by using a fully relativistic distorted-wave method. Special attention is paid to the studies of angular correlations and polarization properties of the 1s2p 3P2 Fi=3/2 1s2 1S Ff=1/2 decay for highly charged He-like Sc19+ and 205Tl79+ ions with nuclear spin I=1/2 following impact excitation by a completely longitudinally-polarized electron beam. Two effects, i.e.the BI and the mutipole mixing between the leading M2 decay and hyperfine-induced E1 decay, on the polarization of the emitted radiation are discussed. Our results show that both the BI and the E1-M2 interference effects may significantly affect the polarization and angular emission pattern of the transition line. For example, the BI and the E1-M2 mixing lead the circular polarization to increase by about 50% and 40% for 205Tl79+ ions, respectively. With the development of the X-ray detectors, the measurement on the polarization during the hyperfine-induced transition becomes feasible. We hope that the present results would be useful in resolving some disagreement between the theories and experiments relating to the polarization properties of the X-ray radiation.

This paper calculates the transition wavelengths and probabilities of the two-electron and one-photon (TEOP) transition from the (3s1/2-1 4dj) J = 1,2 to (3p3/2-1 4s1/2)J = 1 and the (3p1/2-1 4s1/2) J = 1 to (3dj-1 4dj')J = 1,2 for highly charged Ni-like ions with atomic number Z in the range 47 ≤ Z ≤ 92. In the calculations, the multi-configuration Dirac–Fock method and corresponding program packages GRASP92 and REOS99 were used, and the relativistic effects, correlation effects and relaxation effects were considered systematically. It is found that the TEOP transitions are very sensitive to the correlation of electrons, and the probabilities will be enhanced sharply in some special Z regions along the isoelectronic sequence. The present TEOP transition wavelengths are compared with the available data from some previous publications, good agreement is obtained.

A super heavy element Uub (Z = 112) has been studied theoretically in conjunction with relativistic effects and the effects of electron correlations. The atomic structure and the oscillator strengths of low-lying levels have been calculated, and the ground states have also been determined for the singly and doubly charged ions. The influence of relativity and correlation effects to the atomic properties of such a super heavy element has been investigated in detail. The results have been compared with the properties of an element Hg. Two energy levels at wave numbers 64470 and 94392 are suggested to be of good candidates for experimental observations.

Based on the Dirac–Fork–Slater method combined with the multichannel quantum defect theory, the recombination processes of electrons into bare uranium ions (U92+) are investigated in the relative energy range close to zero, and the x-ray spectrum emitted in the direct radiative recombination and cascades processes are simulated. Compared with the recent measurement, it is found that the rate enhancement comes from the additional populations on high Rydberg states. These additional populations may be produced by other recombination mechanisms, such as the external electric-magnetic effects and the many-body correlation effects, which still remains an open problem.

Based on the multi-configuration Dirac–Fock method, theoretical calculations are carried out for the dielectronic recombination (DR) rate coefficients and the collision excitation rate coefficients of Sn10+ ions. It is found that the total DR rate coefficient has its maximum value between 10 eV and 100 eV and is greater than either the radiative recombination or three-body recombination rate coefficients (the number of free electrons per unit is 1021 cm3) for the case of Te > 1 eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dielectronic satellite cannot be ignored at low temperature Te < 5 eV.

The transition energies and electric dipole (E1) transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac—Fock (MCDF) method. In the calculations, the contributions from Breit interaction and quantum electrodynamics (QED) effects (vacuum polarization and self-energy), as well as nuclear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1+ to Np6+ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.

The angular distribution and polarization of the x-ray photoemission of highly charged helium-like ions is studied following the K—LL dielectronic recombination of initially hydrogen-like ions. Calculation is carried out within the framework of the density matrix theory combined with the multiconfiguration Dirac—Fock approach. Attention is paid to magnetic sublevel alignment in the resonant intermediate state and to its nonuniform radiative decay processes. It is shown that the Breit interaction between the incident and target electrons plays a significant role for the alignment of the resonant state and thus causes a substantial change in the x-ray emission characteristic, when compared to the incorporation of only the (non-relativistic) Coulomb interaction. The most prominent difference in alignment parameter is found in the 2s2p1/2 J = 1 resonant state for a wide range of atomic numbers from 9 to 92. For this resonant state of helium-like ions, the Breit interaction becomes significant for ions with nuclear charge Z ~ 30 already.

The differential and integral cross sections for electron impact excitation of lithium from the ground state 1s22s to excited states 1s22p, 1s23l (l = s,p,d) and 1s24l (l = s,p,d,f) at incident energies ranging from 5 eV to 25 eV are calculated by using a full relativistic distorted wave method. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. A part of the cross sections are compared with the available experimental data and with the previous theoretical values. It is found that, for the integral cross sections, the present calculations are in good agreement with the time-independent distorted wave method calculation, for differential cross sections, our results agree with the experimental data very well.

Using multi-configuration Dirac-Fock method and the corresponding packages GRASP92 and RATIP, as well as the newly developed RERR06, we have calculated the radiative recombination (RR) spectra for capturing a continuum electron into n| (n=4—8, l=0—3) subshell of Ni-like Au51+, Cu-like Au50+ and Zn-like Au49+ ions and their corresponding radiative decay spectra. The calculated RR spectra reproduce the experimental spectra excellently. It was found that for the Ni-like Au51+, Cu-like Au50+ and Zn-like Au49+ ions, the probability of capturing a free electron to n=4 subshell is the largest. Furthermore, the main characteristics of the relative decay spectra is the domination of the lines from the captured electrons radiatively decaying from the n=4 subshell.

The electron impact excitation （EIE） cross sections from the ground state to all of the 2s 2 2p 5 3 and 2s2p 6 3（=s, p, d） states along the Ne-like isoelectronic sequence of ions （ Z =50—57） have been calculated by using the multi-configuration Dirac-Fock package GRASP92 and the fully relativistic distorted-wave program REIE06. In the calculations, the relativistic effects and electron correlation effects are considered systematically. Based on those calculations, the EIE cross sections along the Ne-like isoelectronic sequence of ions for different incident electron energies are discussed, and some important conclusions are drawn. We also study the influence of the correlation effects on the values of the 3C/3D line-intensity ratio ［3C: （2p 1/2 3d 3/2 ） 1 →2s 2 2p 6 1 S 0 , 3D: （2p 3/2 3d 5/2 ） 1 →2s 2 2p 6 1 S 0 ］ along the Ne-like sequence. A comparison is made between the present results and previous theoretical calculations and experimental results for the EIE cross sections in Ba46+ ions, and a good agreement is obtained.

Excitation energies and electron impact excitation strengths from the ground states of Ni-, Cu- and Zn-like Au ions are calculated. The collision strengths are computed by a 213-levels expansion for the Ni- like Au ion, 405-levels expansion for the Cu-like Au ion and 229-levels expansion for the Zn-like Au ion. Configuration interactions are taken into account for all levels included. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbits are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. Excellent agreement is found when the results are compared with previous calculations and recent measurements.

Using multi-configuration Dirac-Fock method and the corresponding packages GRASP92 and RATIP, as well as the newly developed RERR06, we calculated inner- and outer-shell photoionization cross sections of configurations 1s2nl(n=2,3; l=s, p) of atomic lithium. In the calculations, the relaxation effect caused by photoionization of electrons was included. It was found that the relaxation effect plays an important role in the inner-shell photoionizational processes, contrary to the outer-shell photoionizational processes. Further, the effects of relaxation on inner-shell photoionizational processes from different states are not the same. It is more prominent for the excited states than the ground state, and for the higher excited states than the lower excited states.

The electron impact excitation(EIE) cross sections of He atom and He-like Fe 24+ , Xe 52+ and U 90+ ions from the metastable 1s2s 3 S 1 to all of 1s nl ( n =2,3; l =s,p,d) states are calculated systematically by using the fully relativistic distorted-wave (RDWB) program developed by our group recently. The effects of the Breit interaction on the EIE cross sections of He-like isoelectronic sequences ions at different energies of incident electrons is studied, and some important conclusions are summarized, which can be extended to other highly charged ions. Also, comparison of the present calculations for 1s2s 3 S 1 →1s2p 3 P and 1s2s 3 S 1 →1s3s 3 S 1 with the available experimental results gave good agreement.

The dielectronic recombination cross sections of Cu18+ ions are calculated using a quasi-relativistic theory. The effects of configuration interaction to the cross sections are analysed. Base on the calculated data, the resonant transfer excitation cross sections of Cu18+ with H2 targets are estimated by using the convolution of Compton profile of the target electron in the impulse approximation. Good agreement of the present calculation with new experimental observation is achieved.

Dielectronic recombination may be regarded as a resonance radiative recombination process. In the process, an incident free electron with given kinetic energy collision with a ion A+q with charge +q, the free electron excited an bound electron of the ion A+q into nl state, and at the same time, itself be captured into another bound state nl, and a resonance doubly excited state will be formed. Furthermore, the state can be stable through radiative photons into some lower states. In this paper, we study the variation of Auger transition rates, radiative transition rates and dielectronic recombination rates with n in (1s1/2εp1/2)- (3s1/2np1/2)0- (n1 l1j1n2l2j2)1 recombination process using relativistic single configuration approximation method. From the method and program set up in this paper, any dielectronic recombination process for any ion can be calculated conveniently.