We have observed the Ba np1/2np and np1/2nd double Rydberg series (n>60,n<0.75n) using a five-laser excitation scheme. A single photon excites the np1/2nl levels from an initially populated Ba 8s1/2nl autoionizing state. If there were no correlation between the two valence electrons, we would observe only the npnp or npnd states. However, we observe strong excitation to nsnl and ndnl states as well. We observe virtually no nsnl and ndnl states for n<0.4n. For n>0.75n the Rydberg structure that is observed for the lower n levels disappears into an apparently unstructured continuum. © 1990 The American Physical Society.
