The high-frequency sound velocity $v_{\infty }$ of liquid water has been determined to densities of $1.37\mathrm{g}/\mathrm{c}{\mathrm{m}}^{\mathrm{3}}$ by inelastic x-ray scattering. In comparison to the hydrodynamic sound velocity $v_0$, the increase of $v_{\infty }$ with density is substantially less pronounced, indicating that, at high density, the hydrogen-bond network is decreasingly relevant to the physical properties of liquid water. Furthermore, we observe an anomaly in $v_{\infty }$ at densities around $1.12\mathrm{g}/{\mathrm{c}\mathrm{m}}^3$, contrasting the smooth density evolution of $v_0$.

• Received 11 April 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.125502