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

摘要

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 μM, pH 2.5-11.3) were acquired in the time range from -50 to 50 μs 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 μs 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 (H_2O_2) and a third component that is assigned to hydroxyl radical (OH) or perhydroxyl radical (HO_2). Furthermore, the pH dependence of the time-averaged concentration of the third components indicates that HO_2 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 H_2O_2, 0.002 to 0.29 for OH, and 0.012 to 0.069 for HO_2.