NEAR-THRESHOLD PHOTOIONIZATION OF ATOMIC BARIUM FROM THE (6S6P)P-1(1)0 STATE

A previous Breit-Pauli R-matrix calculation for photoionisation of the ground state (6s2)1S0 of atomic barium (Bartschat el al., 1986) has been extended to the excited initial state (6s6p)1Po1. Compared with photoionisation from the ground state, the resonance structure is extremely complicated. The theoretical results of approximately 120 Mb near the ionisation threshold are six times larger than those obtained in a Hartree-Slater approximation by Theodosiou (1986), but they are still four times smaller than the experimental data of Kallenbach et al. (1988). However, in view of the difficulties involved in the normalisation of the experimental data, the energy resolution of the experiment, a strong resonance found near threshold, and the qualitative agreement between the shapes of the theoretical and the experimental results, the reasons for the apparent differences in the absolute magnitudes are not clear at the present time.