## Evidence for a quasi-phonon gap in CsCl

Please always quote using this URN: urn:nbn:de:bvb:20-opus-30767
• The observed impurity induced far-infrared absorption in CsCl : Rb$$^+$$ and CsCl : K$$^+$$ is compared with a calculated density of acoustic phonon states in CsCl. The absorption due to CsCl : Rb$$^+$$ displays a minimum between the acoustic and optic phonon bands. A narrow line is observed in CsCl: K$$^+$$ at 85.8 cm$$^{-1}$$ which falls in this quasi-phonon gap.