Infrared Spectra of Lithium Halide Monomers

Abstract

The infrared spectra of the lithium halides have been re‐examined. The vibrational constants of the diatomic molecules are $$\begin{array}{cccc}\mathrm{LiCl}& {\omega }_e\text{=641±3}& {\omega }_e{x}_e\text{=4.2±0.3}& \\ \mathrm{LiBr}& {\omega }_e\text{=563.2±0.2}& {\omega }_e{x}_e\text{=3.53±0.15}& {\omega }_e{y}_e\text{=0.02±0.03}\\ \mathrm{LiI}& {\omega }_e\text{=498.2±0.2}& {\omega }_e{x}_e\text{=3.39±0.15}& {\omega }_e{y}_e\text{=0.08±0.03.}\end{array}$$ The first five coefficients of the Dunham expansion of the potential energy have been obtained for lithium bromide and iodide. Rittner's ionic model has been found to give a good representation of the potential energy. The ionic‐model treatment of the lithium halides has been extended to take account of the higher multipole polarizabilities of the halide ions. The introduction of quadrupole and higher polarizabilities destroys the agreement between observed and calculated spectroscopic constants which is found when only dipole polarizabilities are used.