The spectrum of Y IV was observed in the region from 300 to 5000 Å with the 10.7-m normal-incidence vacuum spectrograph and the 10.7-m Eagle spectrograph in air at the National Bureau of Standards. The light source was a sliding spark discharge. About 560 lines were classified as transitions between 129 energy levels. The observed level system (Kr I isoelectronic sequence) includes nearly all levels of the 4<i>s</i><sup>2</sup>4<i>p</i><sup>6</sup>, 4<i>s</i><sup>2</sup>4<i>p</i><sup>5</sup>5<i>s</i>, 6<i>s</i>, 7<i>s</i>, 4<i>d</i>, 5<i>d</i>, 6<i>d</i>, 4ƒ, 5ƒ, 5<i>g</i>, 6<i>g</i>, and 4<i>s</i>4<i>p</i><sup>6</sup>4<i>d</i> configurations. About 190 lines remain unclassified. All observed configurations have been theoretically interpreted. The energy parameters determined by least-squares fits to the observed levels are compared with Hartree-Fock calculations. The ionization energy as derived from the 4<i>p</i><sup>5</sup><i>ng</i> (<i>n</i> = 5, 6) levels is 488 830 ± 20 cm<sup>-1</sup> (60.608 ± 0.002 eV).
© 1982 Optical Society of America
Gabriel L. Epstein and Joseph Reader, "Spectrum and energy levels of triply ionized yttrium (Y IV)," J. Opt. Soc. Am. 72, 476-492 (1982)