Several authors have described the interaction of ion pairs such as alkylammonium halides with proton donor molecules in aprotic organic solvents sing NMR1,2, mid-infrared2-6or electronic spectroscopy7,8but few far-infrared studies of ion pairmolecule association have been reported in the literature. However, the interaction between alkylammonium halides and benzoic acid9or phenol10has been studied by the far infrared technique and it has been shown that in solvents of low dielectric constant, both cation-anion and anion-molecule stretching vibrations can be simultaneously observed.