Vibrational dynamics of very high density amorphous ice studied by high-resolution x-ray spectroscopy

We report results from high-resolution inelastic x-ray scattering experiments on very high density amorphous (vHDA) water ice samples. The inelastic response of the amorphous structures has been sampled with high accuracy in the momentum Q range of the first pseudo-Brillouin zone. Well distinguished crystal-like phonons have been observed, and excitations of longitudinal and transverse polarization as well as acoustic and optic character are discerned. An averaged longitudinal velocity of sound of about 4050 m/s is established, exceeding the values of high density amorphous (HDA) and low density amorphous ice modifications reported in prior studies. In general, the dynamic features observed in the homogeneous vHDA structure appear to be better resolved and distinguished than the inelastic characteristics found in the heterogeneous structure of HDA.