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Using the Debye shielding model, the effects of plasma shielding on the dielectronic recombination processes of the H-like helium ions are investigated. It is found that plasma shielding causes a remarkable change in the Auger decay rate of the doubly excited 2p 23 P 2 state. As a result, the dielectronic recombination cross sections from the doubly excited 2p 23 P 2 state increases with the decreasing Debye shielding length. [ABSTRACT FROM AUTHOR]

The photoionization cross section of the ground state and the first excited state of C II ions are systematically calculated using the fully relativistic R-matrix code DARC. The detailed resonances are presented and identified for the photon energy ranging from threshold (24.38 eV) up to 41.5 eV where the L-shell (2p, 2s) photoionization process is dominant. In the calculations, the relativistic effect and electronic correlation effect are well considered. It is found that the relativistic effect is very important for the light atomic system CII, which accounts for experimentally observed fine structure resonance peaks. A careful comparison is made between the present results and the experimental values, and also other theoretical data available in the literature, showing that good agreement is obtained for the resonance peaks. [ABSTRACT FROM AUTHOR]

Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56sJ = 2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon. [ABSTRACT FROM AUTHOR]

Electron impact excitation cross sections from the ground state to the individual magnetic sublevels of 1s2p3,1P1 states in high-temperature dense plasmas are calculated for highly charged He-like Fe24+ ions by using a fully relativistic distorted-wave method. The Debye—Hückel screening model is used to screen the projectile electron from the nucleus and target electrons. The linear polarization degrees for these lines are obtained. It is found that the cross sections at all incident energies decrease with the increase of the screening for these excitations. The influence of screening on linear polarization degrees of the 1P1 line is very small. The linear polarization degrees of 3P1 line decrease sharply at low incident energy with the increase of the screening. [ABSTRACT FROM AUTHOR]

Using the density matrix theory and the multi-configuration Dirac–Fock method, the subshell photoionization of highly charged ions is studied, together with their subsequent radiative decay. The effects of polarization transfer on the linear polarization and angular distribution of the characteristic line photoemission for selected Cu-like Zn+, Ba27+, , and ions are investigated. Our results show that the polarization transfer, arising from the originally polarized incident light, may lead to a considerable change in the alignment parameters and the polarization properties of the radiation, the character of which is highly sensitive to the initial photon polarization, yet virtually independent of the photon energy. These characteristics are very similar to those of the electron bremsstrahlung process reported by Märtin et al (2012 Phys. Rev. Lett.108 264801). The present results are compared with available experimental results and show a good quantitative agreement. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The inner-shell 2p3/2 photoionization and the subsequent decay of Mg-like Fe14+, Cd36+, W62+ and U80+ ions are studied theoretically within the multiconfiguration Dirac—Fock method and the density matrix theory. Special attention is paid to exploring the influence of the non-dipole terms which arise from the multipole expansion of the electron-photon interaction in the photoionization process. The results show that the non-dipole contribution to the total cross section, the magnetic sublevels cross section of the photoionization process, the degree of linear polarization and angular distribution of the subsequent characteristic x-ray radiation become more important with the increase of photons energy and atomic nuclear Z. Especially for the cross section and the degree of linear polarization, the non-dipole contribution arrives at 50% for U80+ at four time energy threshold units. However, for the angular distribution, the maximum contribution does not exceed 4%, even for U80+ ions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Detailed calculations using a fully relativistic distorted-wave method incorporating the Debye–Hückel potential are carried out for the electron-impact excitation cross sections from the ground state 1s22s2 (J = 0) to the individual magnetic sublevels of 1s2s22p and states of highly charged Be-like ions in the presence of a plasma environment. The effects of plasma screening on the cross section and linear polarization of the corresponding x-ray emission are investigated. For the line, it is found that the plasma screening has a pronounced effect and causes the cross section to decrease over the whole energy range considered. This dramatic influence also leads to a remarkable decrease in the linear polarization of subsequent x-ray radiation. However, for the line, the plasma screening effect on the cross sections is relatively larger than for the excitations, while its influence on the linear polarization of the radiation is very small. [ABSTRACT FROM AUTHOR]