The adsorption of hexamethyldisilane (HMDS) and trimethylsilane (H-TMS) on graphite monolayers on Pt (111) surfaces was studied with thermal desorption spectroscopy, and the kinetics of reactions of gaseous D atoms with adsorbed H-TMS and HMDS was investigated with reaction product detection techniques. HMDS and H-TMS adsorb and desorb molecularly in the mono- and multilayer regimes. Zero-order desorption indicates that in either regime the molecules tend to agglomerate in islands. Reaction of D atoms with adsorbed HMDS leads via insertion of D into the Si-Si bond to D-TMS products, either adsorbed or as gaseous species, depending on the substrate temperature. D impact-induced abstraction of H from the methyl groups and of methyl from HMDS is much less efficient than D insertion into the Si-Si bond. in accordance with the energetics involved, The reaction kinetics is compatible with an Eley-Rideal mechanism, and a reaction cross-section of sigma = 0.4 Angstrom (2) was obtained. Adsorbed H-TMS does not react with D.