Abstract
High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor of liquid water in the THz frequency range have been performed as a function of wave vector q (1–7 and temperature T (273–473 K), using pressure (0–1.5 kbar) to keep the density at We show that, for the spectra can be consistently explained in terms of a hydrodynamic formalism which includes a viscoelastic, q-independent contribution to the memory function for the density fluctuations. This allows us to extract values for the infinite frequency sound velocity and for the structural relaxation time which are found to compare favorably with those obtained using techniques which probe a lower-frequency range. As a consequence, the atomic dynamics in water is shown to have a homogeneous character down to a length scale of nm. At we find that the viscoelastic contribution to the memory function becomes q dependent. Thus this work provides a view on the evolution of the collective dynamics of water across the q region where the continuum approximation inherent in the hydrodynamic formulation begins to fail. The physical consequences of such a result are discussed in some detail.
- Received 12 April 1999
DOI:https://doi.org/10.1103/PhysRevE.60.5505
©1999 American Physical Society