The Structure of the Third Positive Group of CO Bands

Abstract

The third positive group of CO was photographed under high dispersion. The bands are ${}_{}{}^3{}_{}{}^{}\Sigma \to {}_{}{}^3{}_{}{}^{}\Pi$ transitions. The ${}_{}{}^3{}_{}{}^{}\Sigma$-state shows many strong perturbations. The triplet separation is very small. Of the 15 branches which must be expected under these conditions, 14 are found and traces of the fifteenth. Nine of these branches are strong and can be traced to $K=55\mathrm{}$. The others are weak and present only for small values of the rotational quantum number $K$. The five edges which are characteristic for the bands of the third positive group are formed by the two $O$-branches and the three $P$-branches. The character of the $\Lambda$-doubling and the number of missing lines near the origin shows that the ${}_{}{}^3{}_{}{}^{}\Pi$ state is a normal ${}_{}{}^3{}_{}{}^{}\Pi$ state.