On the Levels of the p²-Configuration in the Arc Spectra of Zn, Cd and Hg

The p² ³P₂ level in the arc spectra of Zn, Cd and Hg has long been considered missing; the accepted explanation has been that transitions involving the level are excessively weakened by auto-ionization. By observation of the arc spectra of these elements in the range 1700-2350 Å, the level in question has been located in Zn and Cd and possibly in Hg. With increasing atomic number auto-ionization increases very greatly, so that one of two diffuse lines in CdI has previously been considered a band of Cd₂. Intensity measurements on this line indicate a natural-broadening profile, and yield a value for the auto-ionization probability.Previous placing of the p² ³P₀ level of HgI is considered erroneous, and a new position suggested.