LAUSR

We investigate the presence of an acoustic-quasi-elastic interaction contribution in the IXS spectra of liquid water at 301K using inelastic x-ray scattering with sub-meV energy resolution at momentum transfers 0.77 ≦ Q ≦ 4.20 nm−1. The contribution appears due to the overlap the acoustic mode with the tail the quasi-elastic mode and is fully consistent with hydrodynamic theory. Incorporating this interaction allows us to describe the dynamic structure factor, SðQ;!Þ, without introducing an extra mode, and may help explain earlier contradictory interpretations. The sound velocity, and relative intensity of the quasi-elastic and acoustic mode, plateau for Q > 2nm−1 at values consistent with a viscoelastic generalization of the Landau–Placzek relation.