Density fluctuations in liquid rubidium. I. Neutron-scattering measurements

We report neutron-scattering measurements of the coherent scattering function S(Q,ω) of liquid rubidium at 315 K, in the range of wave vectors 1.25≤Q≤5.5 ^-1. In this range there is no evidence of peaks at finite ω in S(Q,ω) plotted at constant Q. On the other hand the Fourier transform $F(Q,t)$ exhibits structure, notably for $Q=2.0$ ^-1, which indicates at least two characteristic (wavelength-dependent) relaxation times in the liquid. For wave vectors >3.0 ^-1, $F(Q,t)$ may be characterized by a single relaxation time. These results, in conjunction with our results for $Q<1.0$ ^-1, offer the possibility of detailed comparisons with models of the liquid state and with molecular-dynamics calculations.