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The short-wavelength collective excitations in liquid rubidium at 320 K have been studied by coherent neutron scattering. For values of =2 up to 1. 0 ^-1, clear evidence of propagating modes was found from the shape of the scattering function S (, ) at constant values of. This result shows that the existence of such modes does not depend upon either quantum effects or low thermal population of the modes.
Copley et al. (Mon,) studied this question.