The Y v spectrum has been observed in a sliding-spark discharge with the NBS 10.7-m normal-incidence vacuum spectrograph. The analysis has yielded all the levels of the 4p45s configuration and nearly all levels of 4p44d that can combine with the 4p5 2P ground term. The 4s24p44d + 4s24p45s+4s4p6 levels have been theoretically interpreted, including configuration-interaction effects. The 4s4p62S½ level was found to have a 26% 4s24p44d(1D)2S character and the 4s24p44d(1D)2S½ level a 22% 4s4p62S character. The energy parameters determined from a least-squares fit of the observed level values are compared with Hartree-Fock calculations. The ionization energy is estimated to be 75.0±0.5 eV.
JOSEPH READER and GABRIEL L. EPSTEIN, "Analysis of the Spectrum of Quadruply Ionized Yttrium (Y v)," J. Opt. Soc. Am. 62, 619-622 (1972)