The Translational Lattice-Vibration Raman Spectrum of Single-Crystal Ice Ih

Abstract

We present the Raman spectra in natural and polarized light of ice Ih monocrystals in the region of the translational frequencies. These spectra are of better quality and higher resolution than previous spectra from monocrystals, and demonstrate the value of the investigation of single crystals by this technique, in spite of the proton disorder. In order to explain the observations we use the model of simultaneous activity of the modes allowed in D6h symmetry and the modes allowed by the proton disorder. By analogy with the interpretation of the phenomena observed in ordered piezoelectric crystals, we suggest that the existence of translation frequencies up to c. 320 cm-1 is due to the splitting between transverse and longitudinal optical modes. On this basis, an initial simple dynamical model using only three parameters permits an interpretation of the Raman spectrum. The probable presence of directional effects in ice Ih argues in favour of the proposed explanation.