Velocity-autocorrelation function in liquids, deduced from neutron incoherent scattering results

The Fourier transform $p\left(\omega \right)$ of the velocity-autocorrelation function is derived from neutron incoherent scattering results, obtained from the two liquids Ar and ${\mathrm{H}}_2$. The quality and significance of the results are discussed with special emphasis on the long-time $t^{-\frac{3}{2}}$ tail, found in computer simulations and recent theories. The available experimental data from Na, Ar, and ${\mathrm{H}}_2$ close to their normal melting points are consistent with calculations which take into account the contribution to $p\left(\omega \right)$ from the tail at low frequencies.