Atomic Data for Yb-like Ions from Ta IV to Pt IX Relevant to Tungsten Transmutation in Fusion Plasmas

Accurate atomic data for heavy ions are required for spectroscopic diagnostics and impurity transport modeling in magnetic-confinement fusion devices, particularly for tungsten and its neutron-induced transmutation products. In the present work, we investigate the ytterbium-like ions Ta IV, W V, Re VI, Os VII, Ir VIII, and Pt IX using complementary pseudo-relativistic Hartree–Fock (HFR) and fully relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) approaches. Semi-empirical calculations were first performed using the HFR method including core polarization corrections (HFR+CPOL). The evolution of correlation effects along the isoelectronic sequence was then analyzed through an alternative HFR(CV) model in which the most important core-excited configurations were introduced explicitly to account for core–valence interactions. Extensive least-squares fits to the available experimental energy levels were carried out for all ions considered. The results reveal that the HFR+CPOL approach provides an adequate description of Ta IV and W V, while explicit treatment of core–valence correlations becomes increasingly important from Re VI onwards owing to the growing interaction between the 5d5f and 5p⁵5d³ configurations. New energy level classifications, level compositions, oscillator strengths, and transition probabilities are reported and critically assessed through comparisons between HFR and MCDHF calculations. The resulting dataset extends previous investigations of rhenium and osmium ions and provides benchmark atomic data for heavy-ion spectroscopy and future fusion-plasma applications.