MATRIX SPECTRA OF ION-PAIR SOLVATES, $S_{n} \cdot Li^{+}NO_{3}{^{-}}$

Author Institution: Department of Chemistry, Oklahoma State UniversityThe vibrational spectra of bare ion pairs, such as $Li^{+}NO_{3}{^{-}}$, accurately reflect the magnitude of the cation distortion of the anion through the splitting of otherwise degenerate modes. These large splittings ($262 cm^{-1}$ for $Li^{+}NO_{3}{^{-}}$ in an argon matrix) also provide a useful probe of the effect of cation solvation on the ion pairs since complete solvation, as occurs in liquid solutions of non-dissociating solvents, results in near-collapse of the splitting. The effect of individual solvation steps on the ion pairs can be studied by the measurement of infrared spectra for species such as $S_{1} \cdot LiNO_{3}, S_{2} \cdot LiNO_{3}$ etc. prepared in inert gas matrices containing an appropriate fraction of the solvent, S. High quality FT-IR spectra allow the evaluation of reliable cation solvation numbers, an insight to the nature of the anion-solvent interaction, and an analysis of interplay between cation-solvent bonding and steric forces within the cation solvation shell