R-MATRIX STUDY OF DOUBLE CIRCULAR 4F5G J=3 LEVELS OF BARIUM

The double circular 4f5g J = 3 levels of barium are investigated using the jj-coupled eigenchannel R-matrix method together with the multich annel quantum defect theory. The calculation reproduces well the excit ation spectra of 4f5g J = 3 levels observed recently from the 5d5g J = 2 levels and confirms that the 4f5g levels have low autoionization ra tes. For the first time, excitation spectra calculated using the isola ted-core excitation approximation compared with those determined using dipole matrix elements calculated explicitly within the reaction volu me. The influence of channel mixing on the characteristics of 4f5g J = 3 levels is carefully analysed. Correlation effects are found to be r esponsible for the narrow autoionization widths of 4f5g J = 3 levels. The behaviour of 4f5g levels is compared to that of higher-lying 4fng J = 3 levels.