Chemical Reactions in Liquids:  Photolysis of OClO in Water

The photolysis of aqueous OClO, a key reaction in the understanding of atmospheric photochemistry, was studied using femtosecond spectroscopy. We report experimental results that resolve the current dispute over the chlorine dioxide photolysis and provide a detailed and complete example of chemical reaction dynamics in liquids. Two channels are active in the photolysis: (i) the formation of Cl atoms with a quantum yield of 0.07 ± 0.03 and (ii) the formation of ClO+O, that geminately recombine as a result of caging and forms vibrationally excited OClO, which subsequently relaxes to the vibrational ground state on a 10 ps time scale. By continuously tuning the photolysis wavelengths from 400 to 300 nm, we observe a gradual increase in the cage escape yield, as the kinetic energy of the oxygen atom becomes sufficient to break the solvent cage.