Identification of autoionization thresholds in the cross section for electron ionization of Ba⁺

Recently four thresholds have been reported in the ionization function for the process Ba + +e to Ba 2+ +2e at energies of 15.8, 16.8, 19.2 and 21.9 eV. The excited Ba + states involved have been identified as the 5p 5 5d( 3 P)6s 2 P 1/2 (15.8 eV), 2 P 3/2 (16.8 eV), 5p 5 d( 3 D)6s 2 D 3/2 (19.2 eV) and the combined 5p 5 5d( 1 P)6s 2 P 1/2 and 2 P 3/2 (21.9 eV) states. The identifications are based on Hartree-Fock calculations and intermediate-coupling calculations using scaled Hartree-Fock Parameters. The 5p 5 5d( 3 D)6s 2 D 3/2 threshold at 19.2 eV has a finite electric dipole transition probability to the ground state due to an admixture of 5p 5 5d( 3 P)6s 2 P 3/2 .