Evolution of overlapping resonances along an isoelectronic sequence
  Near-threshold resonances have been studied for Be-like ions with a focus on overlapping resonances among Rydberg series converging to different thresholds. The behavior of the overlapping as a function of Z and the approach to the limit of infinite Z are investigated. The 4s4p resonance is shown and discussed in detail as an example. 
W.-C. Chu, H.-L. Zhou, A. Hibbert, and S. T. Manson
physics.atom-ph