Kinetic models for the generalized Enskog equation

The generalized Enskog equation is used to describe the dynamic structure factor $S(k,\omega )$ for a hard-sphere gas. The problem of constructing kinetic models for the calculation of $S(k,\omega )$ is considered and the minimum set of matrix elements of the exact collision operator required by hydrodynamics is identified. The source of existing discrepancies between kinetic-model calculations and light-scattering experiments is also found and removed. Sensitivity of $S(k,\omega )$ to the parameters of kinetic models is discussed and a simple model proposed. A preliminary comparison of the hard-sphere $S(k,\omega )$ calculated from this model with neutron-scattering data from gaseous krypton is given.