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Abstract

At the TSR storage-ring recombination experiments have been carried out on beryllium-like ions with the merged-beam technique. In addition to the dominant dielectronic recombination (DR), the process of trielectronic recombination (TR) has been observed for N = 0 transitions for the first time. In this case the radiationless electron-capture is accompanied by a simultaneous excitation of two core-electrons. The strength of the TR-cross-section depends strongly on the absence of allowed loss-channels, through which the triply excited intermediate TR-state can decay into the continua of singly excited core-electrons. Along a TR-Rydberg series the resonance{strength drops by several orders of magnitude crossing the DR-series-limits. The experimental spectra show a prefered decay of the core-states to states with identical spin-multiplicity. Thus above the triplet DR-series-limits no triplet TR-resonances and above the singlet DR-series-limits also no singlet TR-resonances can be observed within the experimental sensitivity. Model-spectra calculated with AUTOSTRUCTURE provide a deeper understanding of the process of TR. It could be shown that with increasing nuclear charge the inter-combination selection rule for autoionisation does not strictly hold due to the intermediate coupling. For the heavier ions selection rules can be made out analog to dipole{transition due to the splitting of the singly excited triplet states. The TR-cross{section gets underestimated by theory for higher angular momenta of the valence-electron