The pattern of radiation-induced bond dissociation in alkoxy and siloxy ligands bonded to silica was studied using EPR spectroscopy. Bond-specific damage to ligands was deduced from observation of grafted and physisorbed radicals. Our results show that ligand damage predominates over desorption of ligands from the surface and are consistent with studies of radiation-induced modification of self-assembled monolayers on various types of substrates. Dissociation of C-H bonds is the dominant process, followed by C-C dissociation. In siloxy ligands losses of hydrogen atoms and alkyl groups were both major processes. Direct excitation of dissociative excited states of the organic ligands and ionization are both important damage mechanisms.