Spectroscopy of even-parity autoionizing levels in Ba

Using multiphoton ionization spectroscopy, we have observed transitions in Ba from the 6s2 1S0 ground state to even-parity autoionizing states. We have seen extended series with J = 0, 1, and 2 of the type 5dnd and 5dns, converging on the 5d2D3/2 and 2D5/2 ionization limits. A multichannel quantum-defect theory analysis of the J = 0 spectrum is presented.