Using a crossed-molecular-beam apparatus and a synchrotron as a tunable vacuum-ultraviolet light source, we investigated oxysilanes formed in the reaction of atomic oxygen with silane. We measured the time-of-flight spectra, photoionization yields, and branching ratios of dissociative ionization of reaction products H3SiO/H2SiOH, H2SiO/HSiOH, HSiO/SiOH and SiO as a function of photoionization energy. The observed ionization thresholds correspond to isomeric products H2SiOH, HSiOH, and SiOH. The H-2-loss channel has a branching ratio greater than the H-loss channel for the dissociative ionization of H3SiO/H2SiOH, whereas this situation is reversed for H2SiO/HSiOH, which we interpret according to the enthalpies of reactions. (C) 2007 Elsevier B.V. All rights reserved.