The Spectra of the Calcium I-Like Ions: Manganese VI, Iron VII, Cobalt VIII and Nickel IX

The spectra of four new ions have been added to the sequence of spectra isoelectronic with Ca I. A vacuum spark produced the radiation, which was analyzed in a vacuum spectrograph with a concave grating set for grazing incidence. The transitions observed were those between the ground configuration, 3d^2, and the lowest configuration that combines with it, 3d4p. Nearly all the levels to be expected in these configurations were found, for all four spectra. Almost all the allowed transitions among the observed levels were identified, as were several intercombinations and other forbidden lines. Slater's theory for the levels (neglecting fine-structure) in a configuration gives a good fit with the observed multiplets, especially in 3d4p, which is remote from other odd configurations. In 3d^2, ^1D₂ is evidently perturbed by 3d4s.