Hydridosilsesquioxane-based model systems have been developed over the past five years to help elucidate the structure and reactivity properties of silicon/silicon oxide interfaces; In this paper, the assignment of infrared bands as Si-O or Si-H derived is explored via deuterium labeling studies. In particular, the issue of the presence of adventitious water in the model interfaces is directly addressed via the chemisorption of deuterated-spherosiloxane clusters (D8Si8O12) Onto clean Si(100). The experiments definitively demonstrate that there are no water-derived features detectable by RAIRS in the model interfaces. This rules out water contamination as a possible explanation for the 1.0 eV shifted;feature observed in Si 2p core-level spectroscopy for the model systems. This work is further supported by cluster and water co-dosing experiments on Si(100) which address the spectroscopic sensitivity of surface, silicon-hydrides in this system. Finally, the first Surface crystallographic studies of the mode interfaces performed with LEED are presented. The chemisorbed hydridosilsesquioxane model systems are shown to retain the 2x1 reconstruction of the original Si(100) surface.