Pulse Laser Photolysis of Aqueous Ozone in the Microsecond Range Studied by Time-Resolved Far-Ultraviolet Absorption Spectroscopy

Chemical dynamics of an ozone (O-3) pulse-photolytic reaction in aqueous solutions were studied with pump-probe transient far-ultraviolet (FUV) absorption spectroscopy. With a nanosecond pulse laser of 266 nm as pump light, transient spectra of O-3 aqueous solutions (78-480 mu M, pH 2.5-11.3) were acquired in the time range from 50 to 50 its in the wavelength region from 190 to 225 nm. The measured transient spectra were linearly decomposed into the molar absorption coefficients and the concentration-time profiles of constituted chemical components with a multivariate curve resolution method. From the dependences of the time-averaged concentrations for 20 mu s of the constituted chemicals on the initial concentration of O-3, it was found that the transient spectra involve the decomposition of O-3 and the formation of hydrogen peroxide (H2O2) and a third component that is assigned to hydroxyl radical (OH) or perhydroxyl radical (HO2). Furthermore, the pH dependence of the time-averaged concentration of the third components indicates that HO2 is more probable than OH as the third component. The time-averaged concentration ratio of each chemical component to the initial O-3 concentration depends on the pH conditions from -0.95 to -0.60 for O-3, 0.98 to 1.2 for H2O2, 0.002 to 0.29 for OH, and 0.012 to 0.069 for HO2.