MANY-BODY EFFECTS IN THE 4P SPECTRUM OF STRONTIUM

A new high-resolution study of the 4p spectrum of Sr I at six times the dispersion and resolution available to previous workers is reported. The experiment was performed at the synchrotron radiation laboratory of the 500 MeV accelerator in Bonn. The authors achieve an interpretation consistent with their recent analysis of the corresponding spectrum in Ca I. From the comparison between Ca I and Sr I it emerges, as expected, that there is a progressive fragmentation of the quasi-particle hole with increasing atomic number Z. One can distinguish between two many-body effects, i.e. the N-particle and (N-1)-particle breakdown of the independent-electron scheme; not unexpectedly, the former turns out to grow more rapidly with Z. They also consider the 5p spectrum of Ba I in which they find an extreme breakdown of independent-electron ordering, to the extent that over a significant energy range the interacting energy levels tend towards even spacings (Wigner distribution). © 1990 IOP Publishing Ltd.