Femtosecond movies of water at sub-nanometer lengthscales

The nanometer-scale structure and picosecond-scale dynamics of water are relevant to a wide range of problems in physics, such as the hydrophobic interaction and ion hydration. The behavior of water at these scales has been subject of theoretical and MD studies for decades, and water dynamics has been recently accessed using femtosecond `pump-probe' optical experiments. We will show that it is possible to image dynamical sub-angstrom density fluctuations in water by extracting the density propagator from the dynamical structure factor measured via high-resolution inelastic x-ray scattering spectra at 3$^{rd}$ generation synchrotron sources.