A Study of the Spectra of Columbium and Molybdenum in the Extreme Ultraviolet

The spectra of columbium and molybdenum in the range 100-1000A have been investigated. Spectrograms were obtained with a three-meter grazing incidence vacuum spectrograph having a dispersion of 1.0A/mm at 500A. The lines of Cb V and Mo VI previously reported have been remeasured. Attempts to find higher members of the series $4d-\mathrm{np}$ and $4d-\mathrm{nf}$ have proved fruitless except for the transition $4d-6p$ in Mo VI, for which tentative identification is given. Six low levels of Cb VI and Mo VII have been identified by extrapolation of frequencies in the Kr sequence. Some of the classifications are supported by considerations from theory. By applying a Rydberg formula to the transitions $4p^6-4p^{5}5s$ and $4p^6-4p^{5}6s$, the absolute value of the ground level of Cb VI is estimated to be 829,750 ${\mathrm{cm}}^{-1\mathrm{}}$ and that of Mo VII is estimated to be 1,020,460 ${\mathrm{cm}}^{-1\mathrm{}}$.