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-np and 4d-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 4p⁶-4p⁵5s and 4p⁶-4p⁵6s, the absolute value of the ground level of Cb VI is estimated to be 829,750 cm^-1 and that of Mo VII is estimated to be 1,020,460 cm^-1.The Br sequence has been extended to Cb VII and Mo VIII. The separations of the ground doublets were predicted by use of the regular doublet law. Forty-one lines of Cb VII and forty-two lines of Mo VIII have been identified by extrapolation of frequencies and application of the regular doublet law. These lines arise from transitions between the ground doublet arising from 4s²4p⁵ and the configurations 4s4p⁶, 4s²4p⁴4d, and 4s²4p⁴5s. The absolute values of the ²P^∘3/2 ground levels of Cb VII and Mo VIII are estimated to be 1,005,000 cm^-1 and 1,235,000 cm^-1, respectively.Results of an approximate calculation of the energy levels of the configuration p⁴s in intermediate coupling are given and are compared with the observed levels in Cb VII and Mo VIII. The order of J-values is, with one exception, the same for the calculated levels as for the observed levels. The two sets of levels agree roughly, although the observed levels are more intimately mixed than the calculated levels.