INTERFERENCE EFFECTS IN THE AUTOIONIZATION OF 4F7H AND 6DNI STATES OFBARIUM

In a two-step pulsed laser experiment 4f(5/2)7h J=4,5,6, autoionizing levels of Ba were excited. The 4f(5/2)7h levels interact with 6d(5/2)n i levels resulting in complex interference patterns. The excitation sp ectra were calculated using the eigenchannel R-matrix method in combin ation with multichannel quantum-defect theory. These R-matrix calculat ions reproduce the excitation spectra, including the interference patt erns which involve q-reversal and stabilization against autoionization in the 6d(5/2)ni series, very well. The excitation spectra for J=5 ar e also analyzed using a phase-shifted R-matrix model in which only thr ee channels had to be included to reproduce the main-experimental feat ures. The three-channel model clearly shows that the stabilization aga inst autoionization in the 6d(5/2)ni Rydberg series is a result of int erference in the decay of 4f(5/2)7h and 6d(5/2)ni levels, autoionizing into the same 6d(3/2)epsilon i continuum.