KLL Dielectronic Satellite Spectra from the Photorecombination of He-like Fe and Ni Ions

The radiative decay of a doubly excited autoionizing state is characterized by the dielectronic recombination in the photorecombination (PR) process. We calculate PR cross sections for the ground states of the Fe XXV and Ni XXVII ions by employing the Dirac R-matrix technique. The autoionizing states are treated in the framework of Davies and Seaton's theory to account for the radiative decay. The strengths of the KLL resonances that equate directly to the dielectronic satellite line strengths are evaluated. Besides, the Multiconfiguration Dirac Fock formalism is utilized to obtain the dielectronic satellite line strengths under the isolated resonance approximation. A very good agreement is found for the wavelengths and transition parameters belonging to the KLL autoionizing states with the previous theoretical and experimental results. The dominant KLL dielectronic satellite line strengths from both theoretical models are consistent with each other and are in good agreement with the established theoretical models and measurements at the electron beam ion trap.