Density fluctuations in liquid neon studied by neutron scattering

Abstract

Inelastic neutron scattering experiments have been performed on liquid neon at a temperature of 35 K and pressures of 8 and 14 MPa. The spectra were corrected for all known experimental effects. Normalized results for the coherent dynamic structure factor S(k,ω) were obtained for wave numbers k between 3 and 22 ${\mathrm{nm}}^{\mathrm{-}1}$, all below the position of the first peak, at $k_0$=23.5 ${\mathrm{nm}}^{\mathrm{-}1}$, in the static structure factor S(k). The S(k), calculated by numerical integration of S(k,ω), is compared with neutron diffraction data and with S(k) of argon at corresponding thermodynamic conditions. Quantum corrections to the second frequency moment of S(k,ω) are examined, and a quasiclassical approximation of S(k,ω) is discussed. When comparing S(k,ω) of neon and argon it appears that, except for some small deviations, the principle of corresponding states is valid. The experimental data can well be described by means of one (extended) heat mode and two (extended) sound modes. The sound modes are clearly manifest as shoulders in S(k,ω) which shift, for increasing k, to larger ω and disappear gradually as k approaches $k_0$. The obtained sound dispersion curve, including a sound propagation gap near $k_0$, is consistent with theoretical predictions and with recent results from neutron scattering experiments on argon and from computer simulations. An interpretation in terms of k-dependent transport coefficients is discussed.