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

Abstract

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