Major role of multielectronic K-L inter-shell resonant recombination processes in Li- to O-like ions of Ar, Fe, and Kr

Dielectronic and higher-order resonant electron recombination processes including a K-shell excitation were systematically measured at high electron energy resolution in electron beam ion traps. After storing highly charged Ar, Fe, and Kr ions, the dependence on atomic number Z of the contribution of these processes to the total recombination cross section was studied and compared with theoretical calculations. Large higher-order resonant recombination contributions were found, especially for systems with 10 < Z < 36. In some cases, they even surpass the strength of the dielectronic channel, which was hitherto presumed to be always the dominant one. These findings have consequences for modeling high-temperature plasmas. Features attributed to intershell quadruelectronic recombination were also observed. The experimental data obtained for the He-like to O-like isoelectronic sequences compare well with the results of advanced relativistic distorted-wave calculations employing multiconfiguration Dirac-Fock bound-state wave functions that include threefold and fourfold excitations.