Intershell trielectronic recombination with K-shell excitation in Kr30+

We report the observation of trielectronic recombination with simultaneous excitation of a K-shell and an L-shell electron, hence involving three active electrons. This process was identified in the x-ray emission spectrum of recombining highly charged Kr ions. An energy resolution three times higher than any reported for this collision energy range around 10 keV resulted in the separation of the associated lines from the stronger dielectronic resonances. For Kr30+, intershell trielectronic recombination contributions of nearly 6% to the total resonant photorecombination rate were found.