Characteristic features in photoionization of Fe XIX

Characteristic features of the resonances and background cross sections for photoionization (σ_PI) of oxygen-like iron ion, Fe XIX + hν → Fe XX + e, are demonstrated. The features are introduced by excitations of the core ion to states of n = 2,3,4 complexes in σ_PI of the ground, equivalent electron, and single valence electron excited states. Study from a large number of states is important to establish the general properties of photoionization for complex ions. This is the first detailed study of the ion with a complete set of σ_PI for 900 bound states with n ≤ 10 and l ≤ 9. The ion itself is of great interest for being detected in the x-ray to UV spectra of various astronomical objects. It is found that i) the ground and equivalent electron states have high peak narrow Rydberg resonances in the low energy region corresponding to n = 2 excitations only, ii) for other excited states the resonant features are stronger for core ion excitations to n = 3 complex compared to those for n = 2,4, iii) Seaton resonances due to photo-excitation of the core (PEC) are found most distinct in the energy region for dipole allowed excitation from n = 2 to n = 3 states, and iv) resonances with lower peaks in the energy region between n = 3 and n = 4 excitation indicate convergence. Computations were carried out in the R-matrix method using a large close coupling wavefunction expansion up to orbital 4f and 16 configurations. The present results should provide the data for precise modeling and applications.