Excited electron correlations in resonant multiphoton ionization via barium Rydberg states

Photoelectron angular distributions have been studied in resonant multiphoton ionization of barium via J=0 states, in the region where the 6sns ${\mathrm{}}^1$ $S_0$ Rydberg series interacts strongly with the 5d7d ${\mathrm{}}^3$ $P_0$ doubly excited state. This interaction is dominantly quadrupole and is localized around n=18. The data analysis reveals spin-orbit coupling and strong channel mixing in the continuum.