Low-Lying Even-Parity Resonances in KI:Ag+

Lattice resonances of $E_{\mathrm{g}}$ symmetry (16.35 ${\mathrm{cm}}^{-1\mathrm{}}$) and $A_{1\mathrm{g}}$ symmetry (25 ${\mathrm{cm}}^{-1\mathrm{}}$) have been found in KI:${\mathrm{Ag}}^{+}$ using far-infrared spectroscopic techniques. The two even-parity modes are found to be anharmonically coupled to the $T_{1\mathrm{u}}$-symmetry resonant mode at 17.3 ${\mathrm{cm}}^{-1\mathrm{}}$, giving rise to the combination bands observed at 30 and 44.4 ${\mathrm{cm}}^{-1\mathrm{}}$.