The structures of ozone and HOx radicals in aqueous solution from combined quantum/classical molecular dynamics simulations

Ozone in aqueous solution decomposes through a complex mechanism that involves initial reaction with a hydroxide ion followed by formation of a variety of oxidizing species such as HO, HO2, and HO3 radicals. Though a number of hydrogen-bonded complexes have been described in the gas phase, both theoretically and experimentally, the structures of ozone and HOx in liquid water remain uncertain. In this work, combined quantum/classical computer simulations of aqueous solutions of these species have been reported. The results show that ozone undergoes noticeable electron polarization but it does not participate in hydrogen bonds with liquid water. The main contribution of the solvation energy comes from dispersion forces. In contrast, HOx radicals form strong hydrogen bonds. They are better proton donors but weaker proton acceptors than water. Their electronic and geometrical structures are significantly modified by the solvent, especially in the case of HO3. In all cases, fluctuations in amplitudes of electronic properties are considerable, suggesting that solvent effects might play a crucial role on oxidation mechanisms initiated by ozone in liquid water. These mechanisms are important in a broad range of domains, such as atmospheric processes, plant response to ambient ozone, and medical and industrial applications. (c) 2006 American Institute of Physics.