Atomic structure calculations involving optimization of radial integrals: energy levels and oscillator strengths for Fe XII and Fe XIII 3p-3d and 3s-3p transitions

Abstract

Energy levels and oscillator strengths are calculated for the |$3s^2\enspace 3p^q-3s^2\enspace 3p^{q-1}\enspace3d$| and |$3s^2\enspace 3p^q-3s\enspace 3p^{q+1}$| transition arrays of Fe XII and Fe XIII. Strong configuration interactions are explicitly included in the computations, and the method also involves adjustment of radial energy-integrals F^k, G^k, R^k, in order to minimize differences between observed and calculated energy levels, under the least-squares criterion. It is found that F^k, G^k, R^k integrals need to be reduced from ab init. values (by over 30 per cent for some of the configuration-mixing integrals for Fe XII) and this substantially affects some oscillator strengths. Several spectral lines are newly classified as a result of this analysis. The possible use of empirically adjusted radial-integral values in electron–ion collisional–excitation calculations (as a means of improving the accuracy of target wavefunctions) is discussed.