Far infrared spectroscopic properties and interionic potential energy for tetra-alkylammonium halides

Abstract

The far infrared spectra of solid tetrabutylammonium halides and tetra-isoamylammonium iodide have been investigated. Very strong absorption bands arising from interionic vibrations in the crystal are in evidence. For a series of tetra-alkylammonium halides, a simplified analysis of the band frequencies is presented, based on a model for the ion–ion pair potential energy. The calculated frequencies have been found to be very sensitive to the form of the potential. To account for the experimental data, the energy has to include the contribution of charge-induced dipole interactions. By means of this potential, F.I.R. salt band frequencies can be predicted in solution; they are close to the F.I.R. band frequencies for the solid salt.