Comparison of chlorine dioxide photochemistry in acetonitrile and water using subpicosecond pump–probe spectroscopy

The photochemical reaction dynamics of chlorine dioxide (OClO) dissolved in water and acetonitrile are investigated using subpicosecond pump–probe spectroscopy. The spectral dynamics observed at 267 and 400 nm demonstrate that the quantum yield for geminate recombination of ClO and O to form OClO is reduced in acetonitrile relative to water. However, the dynamics at 800 nm are similar for both solvents consistent with ClOO rather than OClO being responsible for the evolution at this wavelength. The kinetics for ground-state ClOO production and decomposition are significantly slower in acetonitrile relative to water suggesting that solvent–solute hydrogen bonding is important in defining the ground state reactivity of this photoproduct.