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 4s24p6, 4s24p55s, 6s, 7s, 4d, 5d, 6d, 4ƒ, 5ƒ, 5g, 6g, and 4s4p64d 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 4p5ng (n = 5, 6) levels is 488 830 ± 20 cm-1 (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)