Photochemical processes induced by 157-nm light in H 2 -impregnated glassy SiO 2 :OH

F2 excimer-laser irradiation induces two major changes in SiO2:OH glass impregnated with H2 molecules. First, the vacuum–UV optical absorption edge is bleached, and the absorption at 157 nm decreases from 0.95 to 0.68 cm-1. Second, preexisting free SiOH groups and interstitial H2 are photochemically converted to hydrogen-bonded hydroxyl groups. It is suggested that the bleaching of the UV-absorption edge is caused by a change of OH groups from a free to a hydrogen-bonded state and by photolysis of distorted Si—O bonds that are absorbing in the edge region.