PHOTOINDUCED REACTIONS OF OXYGEN-DEFICIENT CENTERS WITH MOLECULAR-HYDROGEN IN SILICA GLASSES

Kinetic trends, pathways, and parameters of the primary and secondary UV photochemical reactions of ''bulk'' and ''surface'' oxygen-deficien t centers (ODC) in silica glasses with molecular hydrogen have been st udied by UV absorption, luminescence, and ESR spectroscopies and the c hemisorption method. The contribution of the singlet and triplet excit ed states of ODC to reaction with hydrogen at different temperatures a nd hydrogen pressures was established for ''surface'' ODC. The activat ion barrier to the H-2 reaction with ''surface'' ODC in the singlet ex cited state was determined as E(a) < 1 kcal/mol. The formation of para magnetic H(I) centers has been observed, The kinetic data observed for ''surface'' ODS photoreactions have been applied to the analysis of s imilar reactions of hydrogen with photoexcited ODC when the diffusion limitations of reaction rates are taken into account. The H(I) centers escaped detection in UV-irradiated ''bulk'' ODC; this is attributed t o the diffusion limitations and subsequent photodecomposition of the H (I) centers.