Isotope shifts in the second negative bands of O 2 +

The second negative bands of O ₂ ⁺ , lying in the region 5000–1850 Å, have been photographed using oxygen enriched in¹⁸O. A study of the isotope shifts in the band heads revealed that thev″ numbering is to be increased by one unit whereas thev′ numbering remains unaltered. This change in vibrational numbering leads to a revision of the molecular constants of O ₂ ⁺ , especially of those in its ground state. These are discussed and the extension of the band system in the vacuum ultra-violet region reported. The possibility of developing a simple spectrographic method for the isotopic assay of oxygen using the isotope shifts in this band system is pointed out. The revised rotational and vibrational constants in theX ² II _g ground state of O ₂ ⁺ molecule are as follows :

$$\begin{gathered} \omega _e = 1903 \cdot 85 cm.^{ - 1} , \hfill \\ \omega _e x_e = 16 \cdot 18 cm.^{ - 1} , \hfill \\ B_e = 1 \cdot 6920 cm.^{ - 1} \hfill \\ and \hfill \\ r_e = 1 \cdot 1161 {\AA}. \hfill \\ \end{gathered} $$