A quantitative study was made of the formation, diffusion and reactions of mobile interstitial H atoms (H0) and molecules (H2) in F2 laser-irradiated silica glass at 10 to 330K. Two key techniques were used: single-pulse F2 laser photolysis of silanol (SiOH) groups to selectively create pairs of H0 and O dangling bonds (non-bridging O hole centers), and in situ photoluminescence measurements of non-bridging O hole centers to monitor their reactions with H0 and H2 as a function of time and temperature. A smaller quantum yield of the photolysis of the SiO-H bond (0.15) as compared with the values reported for gas molecules containing O-H bonds (~1) suggested that the separation of photogenerated H0 from non-bridging O hole centers was hindered by the cage effect of the SiO2 glass network. Distribution functions for the diffusion coefficients of H0 and H2 in the structurally disordered SiO2 glass were evaluated by numerical analysis of the concentration changes in non-bridging O hole centers, based upon diffusion-limited reaction theory. The average diffusion coefficient of H2, obtained by integrating the distribution, agreed well with values which were measured by the permeation of H2 through SiO2 glass plates. In contrast, the average diffusion coefficient of H0 decreased significantly with time because the distribution of the diffusion coefficient of H0 was broad and H0 with greater mobility disappeared at a faster rate. It was suggested that the efficient conversion of H0 into H2 in SiO2 glass was due to dissipation of the excess energy of the reaction intermediate via inelastic collisions with the glass network. The fraction of H0 that formed H2 was determined by the ratio of the capture radii of H0 and non-bridging O hole centers, and was independent of the diffusion coefficient and the initial concentration of H0.

In situ Observation of the Formation, Diffusion, and Reactions of Hydrogenous Species in F2-Laser-Irradiated SiO2 Glass using a Pump-and-Probe Technique. K.Kajihara, L.Skuja, M.Hirano, H.Hosono: Physical Review B, 2006, 74[9], 094202 (11pp)