zThe reaction probabilities of GeH4 and Ge2H6 on the Ge(100) and Ge(111) surfaces have been measured as a function of substrate temperature, incident kinetic energy, and angle of incidence employing supersonic molecular beam scattering techniques. At sufficiently large incident kinetic energies (E(i)> 1 eV) both GeH4 and Ge2H6 react by direct dissociative chemisorption on both surfaces examined, with the reaction probability increasing approximately exponentially with increasing (scaled) incident kinetic energy. At moderate kinetic energies (E(i) similar to 0.4 eV), however, Ge2H6 reacts by a precursor-mediated mechanism on Ge(100), as demonstrated by a decrease in the reaction probability with either increasing substrate temperature or incident kinetic energy, Interestingly, under similar conditions, no evidence is found for precursor-mediated adsorption of Ge2H6 on the Ge(111) surface. The reaction of Ge2H6 does not exhibit a GeH4 production channel on either Ge(100) or Ge(111) for the conditions examined here. The results obtained at high incident kinetic energies (>1 eV) are well described by a statistical model based upon a Rice-Ramsperger-Kassel-Marcus (RRKM) framework. The moderate incident kinetic energy results for Ge2H6 on Ge(100) are well described by a model that assumes reaction via a trapping, precursor-mediated mechanism.