Spectrum and energy levels of triply ionized barium (Ba iv)

The spectrum of Ba iv was observed with sliding sparks and low-inductance vacuum sparks on 10.7- and 3-m normal-incidence vacuum spectrographs. Thirty-nine lines between 463 and 923 Å are classified as transitions between levels of the 5s25p5 2P ground term and levels of the 5s5p6, 5s25p45d, and 5s25p46s configurations. These configurations are theoretically interpreted, and the energy parameters determined from least-squares fits to the observed levels are compared with Hartree–Fock calculations. The ionization energy is revised to 379 300 ± 2700 cm−1 (47.03 ± 0.33 eV).