Note on the Visible Halogen Bands, with Special Reference to ICl

Abstract

It is pointed out that the dissociation of excited IC1 molecules, after absorption of light in the visible bands, into normal atoms is in harmony with theory. In analogy with the other halogens, these bands probably belong to a ${}_{}{}^3{}_{}{}^{}\Pi \leftarrow {}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ transition. The upper level of the bands is, however, doubtless not just the $0^{+}$ part of the ${}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}$ as in the homonuclear halogen molecules, but is probably the whole ${}_{}{}^3{}_{}{}^{}\Pi _0^{}{}_{}{}^{}$, or else the ${}_{}{}^3{}_{}{}^{}\Pi _1^{}{}_{}{}^{}$. Detailed arguments against the possibility that the upper state of the halogen bands may be ${}_{}{}^3{}_{}{}^{}\Sigma$ are given. Conclusions drawn in previous papers from the behavior of the ${\mathrm{I}}_2$ bands in magnetic fields are revised.