FINE-STRUCTURE OF NEGATIVE-IONS OF ALKALINE-EARTH-METAL ATOMS

Fine-structure intervals np1/2-np3/2 (np1/2 is the ground state) are calculated for negative ions using relativistic many-body perturbation theory: Ca- 4p, 56 cm-1; Sr-1 5p, 178 cm-1; Ba- 6p, about 460 cm-1; and Ra- 7p, 1341 cm-1. Comparison of the fine-structure interval with affinity: Ca- 10%, Sr- 22%, Ba- 30%; for Ra- the fine-structure interval is larger than the affinity. Thus the Ra- 7p3/2 state is a resonance in the continuous spectrum with energy 0.018 eV. This means that the relativistic spinorbit interaction plays a determining role in slow electron-radium scattering.