Spectroscopic studies of ion ion interactions.

Current theoretical interpretations of the electronic spectra of solvated halide ions are described and critically discussed. Various consequences of the models are then examined, and compared with experimental results. The effect of ion association on the electronic spectra of several systems is then reviewed, and examples of the analytical methods used to obtain dissociation constants from spectrophotometric data discussed. Brief reviews are given of previous investigations into the effect of anions on the OH stretching frequency of alcohols, and into the ability of carbon tetrachloride to act as an electron acceptor. The spectra of various iodides in several solvents of low polarity have been found to depend upon the identity of the counter-ion, and it is shown that the energies of such spectra have anomalous temperature coefficients. The spectrum of iodide has also been recorded in binary solvent mixtures and the results are discussed in terms of equilibria between free ions, solvent shared ion pairs, and contact ion pairs. The dissociation constant of tetra-n-hexylammonium iodide in dich1oromethane has been evaluated, together with equilibrium constants for the systems n-Hex4NI + cyclo-hex2H2N+ = n-Hex4N+ + cyclo-hex2H2NI in dichloromethane, and n-hex4NI + MeOH = n-hex4NI.MeOH in carbon tetrachloride. This last system has been studied quantitatively by both ultra-violet and infra-red measurements. Finally, the results of the present work are compared with the conclusions drawn from previous conductimetric, N.M.R., E.S.R., and spectrophotometric measurements.