The far infra-red and Raman spectra of the trihalide ions IBr−2 and I−3

The far infra-red spectra of solid samples of tetramethylammonium dibromoiodide and tri-iodide and of their caesium analogues are reported. Solid phase Raman spectra were recorded for the two dibromoiodides using laser excitation. The spectra are discussed and the vibrational frequencies assigned. Force constants were calculated for the dibromoiodide anion. Although the compound of formula (CH3)4 NIBr2 seems to contain a linear anion, the spectra suggest that the caesium analogue does not.