Infrared Absorption Spectrum of Silicon Dioxide

The absorption spectra of fused silica and α‐quartz were investigated in the 2600 to 50 cm −1 wave number region. Only part of the absorption frequency bands of the crystal quartz appeared in the fused state and some of them were shifted to higher wave numbers. The principal absorption frequencies in the fused silica were at 1126, 809, 452, and 200 cm −1 It is proposed that the infrared spectrum of the fused silica results from two vibrating units, of point group T d and D 3 h , simultaneously. In the vitreous state, some of the Si‐O‐Si bonds are disrupted allowing random orientation of the tetrahedral SiO 4 groups (point group T d ). As a consequence of the formation of nonbridging oxygen, the force constant will be increased, as indicated by the shift of the vibrational frequencies to higher values. For every nonbridging oxygen atom formed, the silicon atom previously connected to it would be left with a positive hole. The point group D 3 h is due to such a silicon atom and its v 3 and v 4 modes coincide with the v 3 and v 4 modes of the T d point group.