Spin–orbit transitions (2P1/2←2P3/2) of iodine and bromine atoms in solid rare-gases

Infrared absorptions of iodine and bromine atoms in solid rare-gases are presented. The isolated atoms are produced by UV-photolysis of HI or HBr in solid Ar, Kr and Xe. The absorptions are characterised by sharp zero-phonon lines and broad structured phonon side bands. Some of the zero-phonon lines are resolved and split into two components, separated by a few wavenumbers. The production of the atoms follow second-order kinetics indicating that the primary hydrogen atom undergoes a secondary reaction with the hydrogen halide producing a halogen atom and a hydrogen molecule. This is supported by the observation of the infrared absorptions of hydrogen molecules in concentrated matrices after photolysis.