Influence of hydrogen on paramagnetic defects induced by UV laser   exposure in natural silica
  Diffusion limited reactions of point defects were investigated in amorphous SiO2 exposed to UV laser light. Electron spin resonance and in situ absorption measurements at room temperature evidenced the annealing of E' centers and the growth of H(II) centers both occurring in the post-irradiation stage and lasting a few hours. These transients are caused by reactions involving molecular hydrogen H2, made available by dimerization of radiolytic H0. 
F. Messina, M. Cannas, R. Boscaino