A Strategy for the Analysis of the Far-Infrared Vibrational Modes of Hydrogen-Disordered Ice V

Analysis of the intermolecular vibrational modes in a fingerprint region is always difficult. It is particularly hard to figure out the normal modes, especially in the far-infrared (IR) region, which represent the collective motion of the lattice skeleton. In this study, we determined a strategy for the analysis of a hydrogen-disordered ice phase, ice V. Its phonon density of states and IR and Raman spectra were calculated and verified by experimental data. The focus of this study was to analyze the hydrogen bond (H-bond) vibrational modes in the terahertz region. We used a density functional theory method to develop analytical formulas to prove the existence of two types of H-bond vibrational modes. In the strong mode, the molecules in the lattice vibrate against four neighbors via H-bond stretching, and in the weak mode, the molecules vibrate along two H-bonds between molecules. The ratio of the vibration energy is approximately √2.