Dielectronic recombination rate coefficients of Ni-like barium and tungsten

Ab initio calculations of the total dielectronic recombination (DR) rate coefficient of Ni-like barium (Ba²⁸⁺) and tungsten (W⁴⁶⁺) in the ground state have been performed using the HULLAC atomic code package. Resonant and nonresonant stabilizing radiative transitions are included. Collisional transitions following electron capture are neglected. The present level-by-level calculations include the DR contributions of all of the levels (over 17000) in the Cu-like inner-shell excited configurations 3d⁹4ln′l′ (n′ ≤ 9), 3p⁵3d¹⁰4ln′l′ (n′ ≤ 5), and 3s3p⁶3d¹⁰4ln′l′ (n′ ≤ 5). For both ions, the configuration complexes with a hole in the 3p inner shell contribute almost 10% to the total DR rate coefficient, while the complexes with a hole in the 3s inner shell contribute about 1%. The converging contributions of the 3d⁹4ln′l′ (n′ > 9) configurations are evaluated by applying the complex-by-complex n′^-3; extrapolation method and are found to comprise up to about 20% of the total DR rate coefficients throughout a wide electron temperature range. The total DR rate coefficients are fitted to an easy-to-use analytic expression which reproduces the original data with an accuracy of about 2% or better in a very wide temperature range.