High-pressure reactivity of clathrate hydrates by two-photon dissociation of water.

It is shown that photoinduced reactions are observed at room temperature and pressure of few tenths of gigapascal in clathrate hydrates of CO and of model hydrocarbons under mild irradiation at 350 nm with power in the 50-610 mW range. The reactions are triggered by highly reactive OH radicals produced by two-photon excitation of the lowest electronic excited state of water having dissociative character. The formation of CO(2) is observed in all the reactions involving carbonaceous clathrate hydrates, and direct or indirect evidence for the formation of molecular hydrogen is obtained. The CO(2) produced in the reactions can be sequestered as a clathrate hydrate whose stability range seems to extend to room temperature at pressures of 0.5-0.6 GPa. Although the N(2) hydrate is stable up to 0.9 GPa under irradiation, a partial cleavage of the N-N triple bond is produced once the hydrate decomposes at 0.1 GPa.