Atomic data from the Iron Project - XXXV. Relativistic fine structure oscillator strengths for Fe XXIV and Fe XXV

The first large-scale calculations of relativistic radiative transition probabilities from the Iron Project is reported for dipole allowed and intercombination (El) transitions in Li-like Fe XXIV and He-like Fe XXV. The ab intio calculations are carried out in the close coupling approximation using the Breit-Pauli R-matrix method in intermediate coupling characterized by SLJ, with total (2S + 1) = 2,4. L = 7, J = 1/2 - 11/2 even and odd parity, for Fe XXIV, and with total (2S + 1) = 1,3, L = 9, and J = 0 - 4 for Fe XXV. The eigenfunction expansions for the target ions include 13 levels up to the n = 3 for Fe XXV, and 16 levels up to the n = 4 for Fe XXVI, respectively. The calculated number of bound levels, 83 for Fe XXIV and 138 for Fe XXV, is much larger than experimentally observed. The level energies are in good agreement for the common levels. All dipole and intercombination fine structure transitions involving the calculated bound levels up to n = 10 and l = 5 or 6 are considered. Oscillator strengths, line strengths, and Einstein A-coefficients are tabulated for 802 transitions in Fe XXIV and 2579 transitions in Fe XXV. The results compare well with limited subsets of transitions considered in previous works including fully relativistic and QED corrections. Additional comparisons between the length and the velocity formulations indicate an overall accuracy between 1 - 10%. The range of uncertainty is indicative of the relatively small influence of atomic effects, such as the two-body Breit interaction terms and finite nuclear mass term, that are not included in the Breit-Pauli approximation employed in the present calculations. The extensive set of data is expected to be useful in the analysis of X-ray and XUV spectra from astrophysical sources(1).