Kinetic trends, pathways, and parameters of the primary and secondary UV photochemical reactions of "bulk" and "surface" oxygen-deficient centers (ODC) in silica glasses with molecular hydrogen have been studied by UV absorption, luminescence, and ESR spectroscopies and the chemisorption method. The contribution of the singlet and triplet excited states of ODC to reaction with hydrogen at different temperatures and hydrogen pressures was established for "surface" ODC. The activation barrier to the H-2 reaction with "surface" ODC in the singlet excited state was determined as E(a) < 1 kcal/mol. The formation of paramagnetic H(I) centers has been observed, The kinetic data observed for "surface" ODS photoreactions have been applied to the analysis of similar 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 to the diffusion limitations and subsequent photodecomposition of the H(I) centers.