The solid-solid phase transition of KHF2 was studied by infrared spectrometry at various temperatures and by differential scanning calorimetry(DSC) also. There are hydrogen bonds between the molecules which play a dominant role to the structure at low temperature state. In the temperature range closely corresponding to the solid-solid phase transition, the frequency of antisymmetric stretching(v3) shifted to a higher wavenumber, and the bending(v2) to lower wavenumber. The enthalpy and the temperature of solid-solid phase transition for KHF2 were measured by DSC method and the latter is consistent with the result of IR which could declare the mechanism of solid-solid phase transition of KHF2. With the breaking of hydrogen bonds between the molecules and the introduction of vibrational and rotational disorder KHF2 exhibited crystalline transition.
