In a two-step pulsed-laser atomic-beam experiment we have studied doubly exicted 4fnf series of barium with energy of 11 eV above the atomic ground state (6s2) and 6 eV above the first ionization limit (6s). Starting from 5d2 3F3, 1G4 metastable states, 4f5/2nf J=26 (9n46) states and 4f7/2nf J=36 (n=19, 20, 21, 25, and 40) states were excited using intermediate 5dnf autoionizing Rydberg states. The 4f5/2nf J=2 6 states strongly interact with 4f7/2nf J=2 6 (8 n 20) and 7pn f J=2 5 (6n 10) states. The excitation spectra were analyzed and interpreted using multichannel quantum-defect theory as well as a limited Slater-Condon analysis. The quantum defects of the 4fnf series are large (0.5 1.4), which is an indication for considerable two-electron correlation effects. © 1992 The American Physical Society.