Higher-order resonant inter-shell electronic recombination for heavy highly charged ions

Abstract

Using forced evaporative cooling on stored highly charged ions (HCIs) in an electron beam ion trap, high-resolution electronic recombination spectra were obtained. Inter-shell tri-electronic recombination is reported for HCIs, mainly for C-like ions of Ar, Fe and Kr, where simultaneously with the K-shell excitation an additional L electron is excited at the resonant recombination of a free electron. Clear indications of quadru-electronic recombination are found, where besides the K electron two additional L electrons are excited simultaneously. The experimental technique is described; then the results on first- and higher-order resonant recombination processes are discussed and compared with multi-configuration Dirac–Fock calculations.