The First Spark Spectrum of Caesium (Cs II)

With an electrodeless discharge in a quartz tube the first spark spectrum of caesium has been rephotographed in the region $\lambda 2954.07-\lambda 1857.45$ by means of three sizes of quartz spectrographs. The classifications made by Laporte, Miller, and Sawyer and by Olthoff and Sawyer have been confirmed by additional transitions and used as a basis for extending the classification. Four missing terms in the blended $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)7d,8s$; $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)6d,7s$ configurations have been found, two of these giving rise to resonance lines. The proposed blended configurations $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)8d,9s$; $5p^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)7d,8s$ contain thirteen terms; the $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)10s$, one term, also giving a resonance line; the $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)7p$, six terms; the $5p^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)7p$, three terms; and the $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)nf$, eight terms. In all, 37 levels have been established and 189 lines have been classified. It has also been possible, through the discovery of $f$ terms, to separate the $d$ terms from the $s$ terms of the $5p^5\left({}_{}{}^2{}_{}{}^{}P_{1\frac{1}{2}}^{}{}_{}{}^{}\right)6d,7s$ configuration because of the failure of the $f$ and $s$ terms to combine. The classifications, assignment of inner quantum numbers, and the identification of levels agree with the theoretical considerations as well as with the predictions from the Xe I classification.