Near Infrared Absorption Spectra of Silica: OH Overtones

Water dissolves in fused silica to give hydroxyl groups (OH) which give rise to a fundamental absorption band at 3700 cm−1. The reaction of water with silica may be represented formally as ≡Si-O-Si≡ +H2O→2≡Si-OH. Stevenson and Jack found the extinction coefficient of the above band was 77.5±5.1 mole−1 cm−1. Other less intense absorptions have been observed at 4500 and 7300 cm−1 which are also associated with the presence of hydroxyl groups in fused silica. More recently, Dodd and Fraser have reported the extinction coefficients of the absorption bands at 4500 and 7300 cm−1.