Dielectronic recombination of Ni-like ions through the 3d94ln′l′ (n′=4,5) Cu-like configurations

Ab initio calculations of the rate coefficients for dielectronic recombination (DR) of ten ions along the Ni i isoelectronic sequence in the ground state (${\mathrm{Mo}}^{14+}$, ${\mathrm{Ag}}^{19+}$, ${\mathrm{Xe}}^{26+}$, ${\mathrm{Pr}}^{31+}$, ${\mathrm{Gd}}^{36+}$, ${\mathrm{Dy}}^{38+}$, ${\mathrm{Ta}}^{45+}$, ${\mathrm{Au}}^{51+}$, ${\mathrm{At}}^{57+}$, and ${\mathrm{U}}^{64+}$) through the Cu-like 3${\mathit{d}}^9$4ln′l′ (n′=4,5) inner-shell excited configurations were performed using the h u l l a c code package. Resonant and nonresonant radiative stabilizing transitions and decays to autoionizing levels followed by radiative cascades are included. Collisional transitions following electron capture are neglected. Nonresonant stabilizing transitions are found to enhance the DR rates, and may even dominate the process at low electron temperature. The remarkable difference between the isoelectronic trend of the rate coefficients for DR through 3${\mathit{d}}^9$4l4l′ and through 3${\mathit{d}}^9$4l5l′ is emphasized. The trend of DR through 3${\mathit{d}}^9$4l4l′ shows irregularities at relatively low temperature due to the progressive closing of DR channels as Z increases. Thus, the DR coefficients cannot be reproduced or interpolated by a simple analytical formula. Even for the smooth contributions of the 3${\mathit{d}}^9$4l5l′ configurations, a simplified model using configuration averaging for autoionization and radiative decays instead of level-by-level detailed computations is found to overestimate the DR rates by a factor of up to 2.