Height and density correlations at liquid surfaces; application to X-ray scattering

We calculate height-height correlation functions, near-surface density-density correlation functions and the corresponding frequency integrated spectra for a heat conducting viscous fluid. We calculate scattering cross-sections for the static and dynamic X-ray scattering experiments recently developed to investigate the nanometer-scale structure and fluctuations of liquid interfaces. We show that the density-density correlations make an important contribution to the scattering, even using evanescent waves, and that they are strongly affected by the surface. We also discuss the implications for X-ray photon correlation spectroscopy and X-ray inelastic scattering. (author)