The Spectra of Columbium V and Molybdenum VI

The Rb I-like spectra of columbium and molybdenum have been excited in a vacuum spark and photographed with a vacuum spectrograph. Identifications of lines corresponding to the transitions $5s{}_{}{}^2{}_{}{}^{}S-5p{}_{}{}^2{}_{}{}^{}P$, $5p{}_{}{}^2{}_{}{}^{}P-5d{}_{}{}^2{}_{}{}^{}D$, $5p{}_{}{}^2{}_{}{}^{}P-6s{}_{}{}^2{}_{}{}^{}S$, $4d{}_{}{}^2{}_{}{}^{}D-5p{}_{}{}^2{}_{}{}^{}P$, and $4d{}_{}{}^2{}_{}{}^{}D-4f{}_{}{}^2{}_{}{}^{}F$ for Cb V and Mo VI have been facilitated by extrapolation from the corresponding lines in the spectra of the four preceding elements in the Rb I-like isoelectronic sequence. The relative term values $4d{}_{}{}^2{}_{}{}^{}D$, $5s{}_{}{}^2{}_{}{}^{}S$, $5p{}_{}{}^2{}_{}{}^{}P$, $4f{}_{}{}^2{}_{}{}^{}F$, $5d{}_{}{}^2{}_{}{}^{}D$, and $6s{}_{}{}^2{}_{}{}^{}S$ have been determined. Absolute term values have been approximately fixed by extrapolating ${\nu }^{\frac{1}{2}}$ for the terms of the sequence in such a way as to maintain the validity of the irregular doublet law and they have been compared with those obtained by applying the Rydberg formula to the ${}_{}{}^2{}_{}{}^{}S$ and ${}_{}{}^2{}_{}{}^{}D$ terms, and with those found by extrapolating values of the quantum defects for the ${}_{}{}^2{}_{}{}^{}S$ and ${}_{}{}^2{}_{}{}^{}P$ terms.