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 level was found to have a 26% 4s24p44d(1D)2S character and the level a 22% 4s4p6 2S 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.
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