Single-particle motion in liquid sodium

The van Hove scattering function S(Q,{ω}) of liquid sodium has been measured at three states in the temperature range 400 to 800 K for magnitudes of the scattering vector Q between 0.3 and 4.6 A^-1. Coherent and incoherent scattering were separated by a model analysis. The incoherent data were analyzed in terms of a collision rate and several shape parameters of Sₛ(Q,{ω}) such as the reduced half-width {γ}(Q)=ω1/2(Q)/(DQ)². Results were compared with a kinetic-model theory of G\"otze and Zippelius, showing good agreement. The observed resonancelike transition of {γ}(Q) from a diffusive to a more ``hard-sphere-gas''-like behavior is temperature dependent and indicates no simple relation to the static structure factor of the liquid.