DYNAMICS OF DENSE SUPERCRITICAL NEON AT THE TRANSITION FROM HYDRODYNAMICAL TO SINGLE-PARTICLE REGIMES

The dynamic structure factor, S(Q,E), of neon has been studied by inel astic x-ray scattering and by molecular dynamic simulation in the mome ntum transfer region Q = 1-25 nm(-1) at T = 295 K and P = 3 kbar. At t his density, comparable to that of the liquid at ambient pressure, the shape of S(Q, E) evolves from a Brillouin triplet towards a complex s ingle line shape, which precurs the shape expected for single-particle behavior. The data, analyzed using the three mode model of the molecu lar hydrodynamics, show the absence of positive dispersion in the soun d velocity and a minimum in the dispersion curve.