Interference effects in the autoionization of 4f7hand 6dnistates of barium

In a two-step pulsed laser experiment 4${\mathit{f}}_{5/2}$7h J=4,5,6, autoionizing levels of Ba were excited. The 4${\mathit{f}}_{5/2}$7h levels interact with 6${\mathit{d}}_{5/2}$ni levels resulting in complex interference patterns. The excitation spectra were calculated using the eigenchannel R-matrix method in combination with multichannel quantum-defect theory. These R-matrix calculations reproduce the excitation spectra, including the interference patterns which involve q-reversal and stabilization against autoionization in the 6${\mathit{d}}_{5/2}$ni series, very well. The excitation spectra for J=5 are also analyzed using a phase-shifted R-matrix model in which only three channels had to be included to reproduce the main experimental features. The three-channel model clearly shows that the stabilization against autoionization in the 6${\mathit{d}}_{5/2}$ni Rydberg series is a result of interference in the decay of 4${\mathit{f}}_{5/2}$7h and 6${\mathit{d}}_{5/2}$ni levels, autoionizing into the same 6${\mathit{d}}_{3/2}$εi continuum.