Infrared and Raman spectra of the M+Cl3− ion pairs and their chlorine–bromine counterparts isolated in argon matrices

Abstract

The argon matrix reactions of alkali chloride salts with Cl2 have been investigated through infrared and Raman spectra. In each infrared experiment, an intense product band was observed between 327 and 375 cm−1 and assigned to the antisymmetric stretching vibration ν3 of the Cl3− anion in the ion pair M+Cl3−. Raman spectra of these reaction mixtures yielded the same ν3 bands and, in addition, new signals between 253 and 276 cm−1 which are assigned to the symmetric stretching vibration ν1 of Cl3− in the M+Cl3− species. The observation of two stretching modes in the Raman spectra indicates that the Cl3− ions are asymmetric in these ion pairs. Bromine counterparts and the mixed chlorine–bromine anions were also formed, and used to verify that the anion in the M+X3− species contains three halogen atoms, with the metal ion beside the anion in an asymmetric ’’T’’ shaped structure.