Inelastic x-ray scattering in liquid helium

A detailed experiment and theoretical study of the electronic dynamic structure factor S(k,ω) for 1.6 ^-1≤k≤4.5 ^-1 in liquid helium is reported. A simple hydrogenic theory for the one-electron part of S(→k,ω) is constructed. The theory accounts surprisingly well for the measured S(→k,ω) over the complete range of wave vectors. Two-electron excitations and electron correlation effects thence have at most a minor effect on the dynamic response function.