Abstract
Incoherent, inelastic scattering of neutrons by hydrogen in surface hydroxyl groups has been used to probe the dynamics of 60-70-Å-diameter spheres of amorphous silica. The high-temperature spectra indicate a pronounced "small-particle" enhancement of low-frequency vibrational modes as predicted by theory. At low temperatures, the scattering changes in character and shows evidence of hindered rotational transitions.