In this study we characterize hydrogen diffusion and reaction processes in the near-surface (top 200 Å) of a-Si:H that lead to network equilibration under standard conditions of plasma-enhanced chemical vapor deposition (PECVD). Real time spectroscopic ellipsometry (SE) is used to provide continuous kinetic information on the near-surface conversion of Si-Si to Si-H bonds during exposure of in situ-prepared films at 250°C to filament-generated atomic H. We have found that for optimum PECVD a-Si:H, the formation of additional Si-H bonds is limited by the capture of H at trapping sites, and the rapid diffusion process (D>10-14 cm2/s) by which H reaches the site is not detected optically. Deep trapping occurs at a rate of ∼10 3 s-1 under our filament conditions, estimated to generate ∼1020 cm-3 mobile H in the near-surface of the film. Finally, more than 1021 cm-3 additional H atoms are trapped with emission rates <2×10-7 s-1, suggesting trap depths >2.0 eV. Shallower traps are also detected at lower concentration.