Infrared and spectra of some trihalide ions: ICl−2,IBr−2, I−3, I2Br−, and BrICl−

The Raman spectrum and infrared absorption spectrum have been studied for a number of trihalide compounds. All three fundamental vibrations were located for each trihalide ion and the force constants are given. Differences in the spectra as the cation is changed are attributed to differences in the anion structures and/or differences in the crystal lattice which result in differing selection rules and force constants. The force constants are interpreted as indicating that the bottom of the potential well for the central atom of the trihalide ions is unusually flat. In agreement with previous observations the stretching force constants were found to have a value about half that of the corresponding halogen or interhalogen molecules.