Fine Structure Analysis of the Bands in the A and D Systems of Lead Oxide

Abstract

The bands of the $A$ and $D$ systems of PbO are composed of single $R$ and $P$ branches only. The combination principle has been applied to the lines of these branches and the rotational constants of the molecule have been determined. The bands of PbO have been assigned previously to three systems, $A$, $B$, and $D$, all three having the final state in common. The nuclear separation of this final state is found to be 1.9207 × ${10}^{-8\mathrm{}}$ cm, that of the upper state of $A$, 2.0927 × ${10}^{-8\mathrm{}}$ cm, and of the upper state of $D$, 2.0424 × ${10}^{-8\mathrm{}}$ cm. No $Q$ branches have been found in either of the two systems, indicating that all the electron states involved have the same value of $\Lambda$. It is shown that the electronic levels of the two systems investigated are singlets. All the electron states involved are, in all probability, ${}_{}{}^1{}_{}{}^{}\Sigma$ states.