The Third Spectrum of Krypton

The spectrum characteristic of the ${\mathrm{Kr}}^{++}$ ion has been selected from the various krypton spectra excited in a Geissler tube discharge. The distinction between lines of Kr III or higher spark spectra and those of Kr II is based on the partial or complete suppression of the former by inductance in the discharge circuit. Wavelength measurements, based mainly upon observations with the Rowland grating at the Bureau of Standards, extend from $\lambda 2100$ to $\lambda 7400$. A total of 369 lines has been classified arising from 88 levels of Kr III. The low states of ${\mathrm{Kr}}^{++}$ are ${}_{}{}^3{}_{}{}^{}P$, ${}_{}{}^1{}_{}{}^{}D$ and ${}_{}{}^1{}_{}{}^{}S$, due to the $4s^{2}4p^4$ configuration. The higher excited states are built upon the ${}_{}{}^4{}_{}{}^{}S$, ${}_{}{}^2{}_{}{}^{}D$ and ${}_{}{}^2{}_{}{}^{}P$ states of ${\mathrm{Kr}}^{+++}$ by the addition of $\mathrm{ns}$, $\mathrm{np}$ or $\mathrm{nd}$ to the normal $4s^{2}4p^3$ configuration. All but 8 of the 76 levels comprising the first excited states have been found. The connection between these and the low states has been established by the use of J. C. Boyce's extreme ultraviolet data. Numerous inter-limit combinations have permitted precise evaluation of relative term values. Calculations based on the $4p^3\left({}_{}{}^4{}_{}{}^{}S\right)n{s}^3{S}^0$, and $4p^3\left({}_{}{}^4{}_{}{}^{}S\right)n{d}^3{D}^0$ and ${}_{}{}^5{}_{}{}^{}D_{}^0{}_{}{}^{}$, series have led to an estimated value of 298,020 ${\mathrm{cm}}^{-1\mathrm{}}$ for the lowest $4p^4\left({}_{}{}^4{}_{}{}^{}S\right){}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ level, corresponding to an ionization potential of 36.8 volts.