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${̊}^{\mathrm{-}1}$. 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 $S_s$(Q,ω) such as the reduced half-width γ(Q)=${\omega }_{1/2}$(Q)/(DQ${)}^2$. Results were compared with a kinetic-model theory of Götze 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.