Quantum-Mechanical Calculations of the Infrared Properties ofH−Ions in Potassium Halides

The infrared properties of the ${\mathrm{H}}^{-}$ ion in KCl, KBr, and KI are studied using force constants obtained from quantum-mechanical calculations of the electronic structure of the $U$ center. The anharmonic sidebands of the ${\mathrm{H}}^{-}$ local mode and the induced far-infrared absorption are calculated. In most cases the calculated force-constant changes give results comparable to the parametrized values used in previous work. It is emphasized that the force-constant changes in $A_{1g}$, $E_g$, and $T_{1u}$ displacements are not generally equal. Occasionally, features not found in previously published experimental or theoretical work are observed. Repulsive Born-Mayer potentials for the ${\mathrm{H}}^{-}$-${\mathrm{K}}^{+}$ interaction in the three crystals are extracted from the quantum-mechanical calculations. Our techniques for handling the numerical evaluation of Green's functions are discussed briefly.