Abstract. Effective recombination coefficients are given for C ii transitions between doublet states. The calculations are carried out in the temperature range 500 − 20 000 K and for an electron density of 10 4 cm −3 . The effects of electron collisions on the excited states are included. The necessary bound-bound and bound-free radiative data are obtained from a new R-matrix calculation in which photoionization resonances are fully delineated, thereby accurately incorporating the effects of both radiative and dielectronic recombination. The R-matrix calculation includes all bound states with principal quantum number n ≤ 15 and total orbital angular momentum L ≤ 4. The effect of moving the resonance features to their experimentally determined positions is also investigated and found to be important at low temperatures.

Abstract. We calculate effective recombination coefficients for the formation of selected lines of N ii. New photoionization data are computed which accurately map the near threshold resonances and are used to derive recombination coefficients for principal quantum numbers, n ≤ 15, including radiative and dielectronic recombination. Cascading from higher states is included, allowing for the effects of finite electron density in a hydrogenic approximation. The effects of population in the excited states of the recombining ion are investigated.

Abstract. We calculate total recombination coefficients for Ne 2+ + e − and effective recombination coefficients for the formation of selected lines of Ne ii. New photoionization data are calculated which accurately map the near threshold resonances and are used to derive recombination coefficients for principal quantum numbers, n ≤ 15, including radiative and dielectronic recombination. Cascading from higher states is included, allowing for the effects of finite electron density in a hydrogenic approximation. The effects of population in the excited states of the recombining ion are investigated.

The charge state distributions of Fe, Na, and F are determined in a photoionized laboratory plasma using high resolution x-ray spectroscopy. Independent measurements of the density and radiation flux indicate unprecedented values for the ionization parameter xi=20-25 erg cm s(-1) under near steady-state conditions. Line opacities are well fitted by a curve-of-growth analysis which includes the effects of velocity gradients in a one-dimensional expanding plasma. First comparisons of the measured charge state distributions with x-ray photoionization models show reasonable agreement.

Magnetic dipole transitions between the levels of ground 4d N configurations of tungsten ions were analyzed by employing a large basis of interacting configurations. Previously introduced configuration interaction strength between two configurations was used to determine the configurations with the largest contribution to wave functions of atomic states for the considered configurations. Collisional-radiative modeling was performed for the levels of the ground configuration coupled through electric dipole transitions with 4p 5 4d N+1 and 4d N−1 4f configurations. New identification of some lines observed in the electron-beam ion trap plasma was proposed based on calculations in which wavelength convergence was reached.

The contribution to electron-impact ionization cross sections from excitations to high-nl shells and a consequent autoionization is investigated. We perform relativistic subconfiguration-average and detailed level-to-level calculations for this process. Ionization cross sections for the W27+ ion are presented to illustrate the large influence of the high shells (n ^ 9) and orbitals (/ > 4) in the excitation-autoionization process. The obtained results show that the excitations to the high shells (n ^ 9) increase cross sections of the indirect ionization process by a factor of 2 compared to the excitations to the lower shells (n < 8). The excitations to the shells with orbital quantum number l = 4 give the largest contribution compared with the other orbital quantum numbers /. Radiative damping reduces the cross sections of the indirect process approximately twofold in the case of the level-to-level calculations. Determined data show that the excitation-autoionization process contributes approximately 40 % to the total ionization cross sections.

Absorption-line spectroscopy is a powerful tool used to estimate element abundances in the nearby as well as distant universe. The accuracy of the abundances thus derived is, naturally, limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform the new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state-of-the-art quantal calculations. Here we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts (GRBs). We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-ralativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (≈ 0.04 dex) to the metallicities estimated from S II in past studies. These results will be readily applicable to other studies of S II in the Milky Way and other galaxies.

Effective collision strengths for forbidden transitions among the five energetically lowest fine‐structure levels of O ii are calculated in the Breit–Pauli approximation using the R‐matrix method. Results are presented for the electron temperature range 100–100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O ii ratio, a matter of some recent controversy. Finally, we present plasma diagnostic diagrams using the best collision strengths and transition probabilities.