Raman spectrum and structure of silica aerogel

Raman spectra have been obtained from silica aerogel, a porous low‐density material having grain sizes near 70 A. The Raman spectra are qualitatively similar to those from fused silica, thus indicating that the aerogel is amorphous. However, a greatly intensified peak (relative to ordinary fused silica) occurs near 478 cm−1 and is assigned to small rings, e.g., six (3‐SiO) or eight (4‐SiO) membered. Such rings may be more important in the aerogel than in fused silica, but the observed absence of the 600 cm−1 ring peak indicates that only one ring type, e.g., eight membered, is predominant. Other marked frequency and intensity changes in the Si–O–Si bending and Si–O stretching region, compared to fused silica, were also observed.