Fine-structure energy levels and lifetimes in Al-like iron and nickel

Large-scale CIV3 calculations are performed for the excitation energies from the ground state for 53 fine-structure levels as well as for some oscillator strengths and radiative decay rates for electric-dipole allowed and intercombination transitions among the levels of the terms (1s(2)2S(2)2p(6))3S(2)3p(P-2(o)), 3s3p(2)(S-2, (2)p, D-2, (4)p), 3S(2)3d(D-2), 3p(3) (4S(o), P-2(o), D-2(o)), 3s3p(P-3(o))3d(P-2(o), D-2(o), F-2(o), P-4(o), D-4(o), F-4(o)), 3s3p(P-1(o))3d(P-2(o), D-2(o), F-2(o)), 3s(2)4s(S-2), 3S(2)4p(P-2(o)), 3S(2)4d(D-2), 3s(2)4f(F-2(o)), 3s3p(P-3(o))4s((2)p(o), (4)p(o)) and 3s3p(P-1(o))4s((2)p(o)) of Fe xIv and Ni xvI. In this calculation, a large number of configurations which include up to n = 5 orbitals are used to ensure convergence. The important relativistic effects in intermediate coupling are incorporated by means of the Breit-Pauli Hamiltonian. Our calculated excitation energies, including their ordering, are in excellent agreement with the available experimental results for both Fe xiv and Ni xvi. We also predict new data for NixvI for the levels arising from the configurations with n = 4 orbitals where there are no theoretical or experimental results available. From our transition probabilities, we have calculated radiative lifetimes of the high-spin levels 3s3p(2) P-4 and 3s3p3d F-4(o). A large difference in the lifetime (about a factor of four) of the latter level of Fe xiv between our calculated value (using our adjusted energies), on the one hand, and the experimental result of Trabert et at and other theoretical calculations, on the other hand, is explained through subtleties in the energy values. The new predicted lifetime for the 3s3p3d F-4(3/2) level of Fe xiv could have interesting implications for ion laser investigations.