Resolution of the long-standing overprediction of the resonance to intercombination line-intensity ratio in mid-Z neonlike ions

The Ne-like resonance 2p^6 1S-2p⁵3d ¹P (3C) to intercombination 2p^6 1S-2p⁵3d ³D (3D) line-intensity ratio, R(3C∕3D), has been extensively studied through high-accuracy measurements and calculations of atomic structure and collision cross sections. However, even state-of-the-art relativistic multiconfiguration atomic-physics codes generally predict values of R(3C∕3D) that are significantly larger than those observed in coronal-density experiments. In this paper, predictions of R(3C∕3D) across the Ne-like isoelectronic sequence from chromium to silver are brought into agreement with coronal-density experimental measurements in two steps: first by including a semiempirical correction in the collisional atomic data due to configuration-interaction effects, and next by including the effects of cascades on the upper level populations. The configuration-interaction correction is inspired by the observation that nearly all data-production codes fail to predict R(3C∕3D) correctly and is justified theoretically by a careful analysis of configuration-interaction contributions to level energies. The dependence of R(3C∕3D) with electron density and its agreement with moderate-density measurements are shown. A brief description of the application of our technique to line ratios in He- and Ni-like x-ray spectra is also given.