The bonding state of OH groups in silica glasses is studied by examini
ng infrared absorption spectra and thermal annealing characteristics o
f gamma-induced paramagnetic detect centers. When an oxygen-rich silic
a is treated by hydrogen, OH groups exist in the form of those hydroge
n-bonded with nonbridging oxygen (=Si-O- --- -H-O-Si=) besides the for
ms of H2O and =Si-O-H.