The First Spark Spectrum of Rubidium (Rb II)

The resonance lines of Rb II have been photographed in the extreme ultraviolet region with the vacuum spectrograph. The mode of excitation was the hollow cathode discharge in helium, and in addition, the hot spark was employed with rubidium hydroxide in cored aluminum electrodes. The values of the wave-lengths of the ultraviolet lines for Rb II were obtained from third order measurements. The visible region was photographed with various glass and quartz spectrographs. With the separations of the resonance lines as guides, the classification scheme given by Reinheimmer was found to be correct, but incomplete. Some lines taken from Otsuka's data were fitted into the scheme. The coupling is of an intermediate type approaching that of ($\mathrm{jj}$) form. Levels of the $4p^{5}4d$, $4p^{5}5s$, $4p^{5}5p$, $4p^{5}5d$, and $4p^{5}6s$ configurations were identified. Their separations were compared with Kr I. It was also attempted to separate the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ terms due to $4p^5(5s, 6s)$ from the $4p^5(4d, 5d)$ levels. The limit of excitation furnished by metastable helium falls exactly between the various levels caused by the $4p^{5}5p$ configuration, thus providing a check on the interpretation of the classification. The ionizing potential of Rb II was calculated to be 27.3 volts.