The polarized Raman and i.r. spectra of KHF2

A comprehensive polarized i.r. and Raman study is reported on single crystals of potassium dihydrogen fluoride and its deuterated counterpart. All the group-theoretically predicted zero wave-vector modes have been observed and assigned to specific modes of vibration. The real and imaginary components, ε′ and ε″, of the dielectric constant have been calculated from the reflection measurements by means of Kramers—Kronig analysis and by classical oscillator fitting procedures both parallel and perpendicular to the crystal c-axis. The half-width of the antisymmetric hydrogen bonded bifluoride ion vibrational band is found to be about 40 cm−1 which is much smaller than has previously been reported in the literature. The absorption coefficient has been obtained from transmission studies. A small contraction of the HF bond length on deuterium substitution has been confirmed through its effect on the symmetric stretching Raman frequency and some calculations on the anharmonicity of the hydrogen bond, which is responsible for this effect, are presented. Raman spectra have also been obtained of NaHF2 powder specimens and of a saturated aqueous solution of HF2−.