The spectra of Cs III, Ba IV, and La V have been observed in a sliding spark discharge on the 10.7 m normal-incidence vacuum spectrograph at NBS. Analysis of the observations of Cs III and La V has yielded the energy levels of the 5s²5p⁵ and 5s5p⁶ configurations and nearly all levels of the 5s²5p⁴5d and 5s²5p⁴6s configurations that can combine with the 5s²5p⁵²P° ground term. The observations for Ba IV have yielded the levels of the 5s²5p⁵ and 5s5p⁶ configurations. The 5s²5p⁴5d + 5s²5p⁴6s + 5s5p⁶ levels of Cs III and La V have been theoretically interpreted, with configuration interaction included. The energy parameters determined from a least-squares fit to the observed level values are compared with Hartree-Fock calculations. The ionization energies are found to be 33.38 ± 0.25 eV for Cs III, 47.1 ± 0.6 eV for Ba IV, and 61.6 ± 0.6 eV for La V. By extrapolating these values the ionization energy of Ce VI is estimated as 77.6 ± 1.2 eV.

© 1976 Optical Society of America

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