In this work, we investigate the origin of a giant isotope effect discovered in the blistering of hydrogen-ion-implanted and annealed silicon. Si(001) samples were implanted or coimplanted with 5 keV of H and/or D ions to total fluences of 2x10(16) and 6x10(16) ion/cm(2). The lower fluence is sufficient for blistering by pure H, but the higher one is required for the maximum blister coverage whenever D is involved. On these samples, we carried out Raman-scattering investigations of the evolution of Si-H/D complexes upon a stepwise thermal annealing from 200 to 550 degreesC. We have identified the critical chemical transformations characterizing the hydrogen-deuterium-induced blistering of silicon. The puzzling dependence on ion mass appears to be mainly connected with the nature of the radiation damage. We have found that H is more efficient in "preparing the ground" for blistering by nucleating platelets parallel to the surface, essentially due to its ability to agglomerate in the multihydride monovacancy complexes that evolve into hydrogenated extended internal surfaces. By contrast, D is preferentially trapped in the surprisingly stable monodeuteride multivacancies. (C) 2004 American Institute of Physics.