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 5s²S-5p²P, 5p²P-5d²D, 5p²P-6s²S, 4d²D-5p²P, and 4d²D-4f²F 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 4d²D, 5s²S, 5p²P, 4f²F, 5d²D, and 6s²S have been determined. Absolute term values have been approximately fixed by extrapolating ν1/2 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 ²S and ²D terms, and with those found by extrapolating values of the quantum defects for the ²S and ²P terms.