Ultra-Ionization Potentials in Mercury Vapor

It is shown that Takamine's new ${}_{}{}^3{}_{}{}^{}{P}_2_{}^0{}_{}{}^{}$ level in Hg I is probably the lowest level from the structure $d^9{s}^{2}p$. The positions of the other levels are discussed and it is shown that some of them will be negative. The phenomenon of auto-ionization is described and its effect on the negative terms is suggested as the cause for the existence of ultraionization potentials. Some remarks are made regarding perturbed series.