Vibrational modes in silica aerogels: low-frequency Raman scattering

Low-frequency Raman scattering was observed from different silica aerogels obtained from hydrolysis of tetramethoxysilane in alkaline conditions. It is deduced that the diameter of cylindrical chains of the network is 50 or 70 AA, depending on the origin of the aerogel. These experimental results are interpreted on the basis of Raman scattering from fractal vibrations in spherical structural units for base-catalysed aerogels.