Relativistic photoionization cross sections for C II

High resolution measurements of photoionization cross sections for atomic ions are now being made on synchrotron radiation sources. The recent measurements by Kjeldsen etal. (1999) showed good agreement between the observed resonance features and the the theoretical calculations in the close coupling approximation (Nahar 1995). However, there were several observed resonances that were missing in the theoretical predictions. The earlier theoretical calculation was carried out in LS coupling where the relativistic effects were not included. Present work reports photoionization cross sections including the relativistic effects in Breit-Pauli R-matrix (BPRM) approximation. The configuration interaction eigenfunction expansion for the core ion C III consists of 20 fine structure levels dominated by the configurations from 1s^22s^2 to 1s^22s3d. Detailed features in the calculated cross sections exhibit the missing resonances due to fine structure. The results benchmark the accuracy of BPRM photoionization cross sections as needed for recent and ongoing experiments.Comment: 13 pages, 3 figure

Relativistic close coupling calculations for photoionization and recombination of Ne-like Fe XVII

Relativistic and channel coupling effects in photoionization and unified electronic recombination of Fe XVII are demonstrated with an extensive 60-level close coupling calculation using the Breit-Pauli R-matrix method. Photoionization and (e + ion) recombination calculations are carried out for the total and the level-specific cross sections, including the ground and several hundred excited bound levels of Fe XVII (up to fine structure levels with n = 10). The unified (e + ion) recombination calculations for (e + Fe XVIII --> Fe XVII) include both the non-resonant and resonant recombination (`radiative' and `dielectronic recombination' -- RR and DR). The low-energy and the high energy cross sections are compared from: (i) a 3-level calculation with 2s^2p^5 (^2P^o_{1/2,3/2}) and 2s2p^6 (^2S_{1/2}), and (ii) the first 60-level calculation with \Delta n > 0 coupled channels with spectroscopic 2s^2p^5, 2s2p^6, 2s^22p^4 3s, 3p, 3d, configurations, and a number of correlation configurations. Strong channel coupling effects are demonstrated throughout the energy ranges considered, in particular via giant photoexcitation-of-core (PEC) resonances due to L-M shell dipole transition arrays 2p^5 --> 2p^4 3s, 3d in Fe XIII that enhance effective cross sections by orders of magnitude. Comparison is made with previous theoretical and experimental works on photoionization and recombination that considered the relatively small low-energy region (i), and the weaker \Delta n = 0 couplings. While the 3-level results are inadequate, the present 60-level results should provide reasonably complete and accurate datasets for both photoionization and (e + ion) recombination of Fe~XVII in laboratory and astrophysical plasmas.Comment: 19 pages, 8 figures, Phys. Rev. A (submitted

ELECTRON SCATTERING FROM HYDROGEN ATOMS AND H-LIKE IONS

Cette revue pour l'"Atomic Data Workshop" de Meudon (1-2 septembre 1989) est une mise à jour de l'atelier précédent (St. Catherine's College Oxford, 1987) pour ce qui est des données sur la diffusion des électrons par les atomes d'hydrogène et les ions hydrogénoïdes. Pour l'hydrogène, le nouveau calcul "Intermediate Energy R-Matrix" (IERM) de Scholz et al. devient la source recommandée de taux d'excitation pour les transitions 1s-2s et 1s-2p ; pour les ions hydrogénoïdes multichargés, les formules semi-empiriques de Sampson et Zhang sont recommandées.This review, for the "Atomic Data Workshop" held at Meudon 1-2 September 1989, provides an update on the last Workshop (at St Catherine's College Oxford, 1987) for data on electron scattering from hydrogen atoms and H-like ions. For hydrogen, the new "Intermediate Energy R-Matrix" (IERM) calculation by Scholz et al becomes the recommended source of excitation rates for the 1s - 2s and 1s - 2p transitions ; for highly charged H-like ions Sampson and Zhang's semiempirical formulae are recommended