4p54d2configuration of Mo vi

The internally excited 4$p^5$4$d^2$ configuration gains notoriety in the Rb isoelectronic sequence from Y i i i onwards for appreciably disturbing levels of the nf and np series of the one-electron spectra. We have worked out, on the basis of the spectra recorded in collaboration with J. O. Ekberg at Lund University and with the help of R. D. Cowan’s computations, transitions from this configuration to the ground configuration 4$p^6$4d. Of the 45 levels of 4$p^5$4$d^2$, all 38 that can combine with 4$p^6$4d are established. Many levels of 4$p^5$4$d^2$ are computed to be highly mixed within the configuration, as well as with levels of 5f ${}^2$F, 4f ${}^2$F, 6p ${}^2$P, and 5p ${}^2$P in descending order of magnitude. This is evidenced experimentally by the observation of transitions connecting some 4$p^5$4$d^2$ levels with those of ns, nd (other than 4d), and ng.