Low-Lying Doubly Excited States of the Helium Isoelectronic Series

Abstract.

 We present within the hyperspherical adiabatic approach a nonadiabatic calculation of the low-lying doubly excited states for heliumlike atomic systems with Z ranging from 2 to 6. Potential curves, channel functions, and nonadiabatic couplings are accurately obtained using a well-established technique. By neglecting the lowest potential curve of each system, the doubly excited states are identified as bound states of the remaining coupled closed channels. We investigate the efficacy of this approximation by comparing the resonance positions with the values obtained when the coupling with the neglected open channel is included in the calculation.