First Spectra of Chlorine, Bromine, and Iodine in the 4-μm Region*

A description of the spectra of the halogens, Cl i, Br i, and I i, in the 4-μm region, is presented. The observed transitions consist almost exclusively of the 4f–5g transitions. Essentially pure pair coupling is realized in the instance of the g levels. The analysis is based on theoretical energy expressions, and the agreement between observed and calculated energy-level distributions is demonstrated.