The formation of H adducts during radiolysis of zeolites containing olefinic and aromatic hydrocarbon guests was demonstrated to occur by H atom transfer from the zeolite to the adsorbed molecules. The H adducts and other paramagnetic radiolysis products (radical cations and H-loss radicals) were detected by EPR spectroscopy. The mechanism of H adduct formation was confirmed by, inter alia, H/D isotopic labeling and comparison of results in HZSM5 and H−Mordenite to results in their Na+-exchanged counterparts. The effects of charge transfer among radiolysis products and zeolite−adsorbate interactions on the relative yields of trapped species is discussed. It is proposed that molecules smaller that a critical size adsorb inhomogeneously in ZSM5, forming aggregates in which ion−molecule reactions occur. Interpretation of the experimental results was aided by quantum chemical calculations of the molecular properties of the intermediates and their reaction energetics. This included evaluation of electron-transfer exothermicities, activation energies for H addition, and the relative acidities of the radical cations.

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.

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