Electron‐Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. IX. Ni xxvi and Ni xxvii for Ultraviolet and X‐Ray Modeling

The inverse processes of photoionization and electron-ion recombination of ( h ν + Ni ↔ Ni + e ) and ( h ν + Ni ↔ Ni + e ) are studied using the unified method for the total recombination. The method subsumes both the radiative and dielectronic recombination processes and enables self-consistent sets of results for photoionization and electron-ion recombination by using the same wavefunction for these inverse processes. Photoionization cross sections (σ PI ), recombination cross sections (σ RC ), recombination collision strengths (Ω RC ), and recombination rate coefficients (α RC ) are obtained for ionization balance and spectral analysis of UV and X-ray lines. Level-specific photoionization cross sections and recombination rates are presented to enable accurate computation of recombination-cascade matrices for all fine-structure levels n (ℓ SLJ ) up to n ≤ 10 : 98 bound fine-structure levels of Ni XXVI with 0 ≤ l ≤ 9, 0 ≤ L ≤ 11, and 1/2 ≤ J ≤ 17/2, and 198 levels of Ni XXVII with 0 ≤ l ≤ 9, 0 ≤ L ≤ 14, and 0 ≤ J ≤ 10. Total α RC -values for Ni XXVI and Ni XXVII are compared with the existing values and are found to be in very good agreement. Total recombination rate coefficients for the hydrogen-like recombined ion, Ni XXVIII, are also presented. The calculations are carried out in the relativistic Breit-Pauli R -matrix (BPRM) approximation with inclusion of radiation damping of resonances. With consideration of all details of the processes, the results, which include the level-specific σ PI and α RC calculated for the first time, should be the most accurate for these ions.