Resonance lines and energy levels of Cs iii, Ba iv, and La v

Abstract

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 5s25p5 2P° 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.