SPIN-ORBIT EFFECTS IN THE HEAVY ALKALINE-EARTH ATOMS

Complex bound and autoionizing spectra of strontium, barium, and radium are treated at two different levels of approximation using multichannel-quantum-defect techniques (MQDT) and eigenchannel R-matrix calculations. In the first level, the R-matrix calculations are conducted entirely in LS coupling without explicitly including any spin-orbit terms in the Hamiltonian. A subsequent frame transformation to jj coupling is then carried out prior to the MQDT treatment. In the second level, the entire R-matrix calculation is conducted in jj coupling, including spin-orbit terms in the Hamiltonian explicitly within the R-matrix box. The two methods give nearly identical results even for atoms as heavy as barium, each showing good agreement with experiment, but significant differences begin to appear between the two levels of approximation for atomic radium.