[2] Pulse radiolysis in study of oxygen radicals

Pulse radiolysis is accomplished by a combination of a pulsed-radiation generating machine (electron accelerator) and a variety of time-resolved detecting systems. In many respects, pulse radiolysis, in which free radicals are generated by ionizing radiations, is similar to laser and flash photolysis, in which free radicals are generated by photonic processes. In this chapter, pulse radiolysis studies of hydroxyl, peroxyl, superoxide, alkoxyl, and phenoxyl radicals, as well as their properties are discussed. Free radical absorption spectra are usually red shifted compared with parent compounds, an important feature in monitoring. The spectra can be obtained point by point by measuring absorption at different wavelengths selected by a monochromator at a constant dose/pulse. The absorbances are calculated from actual concentrations of radicals corresponding to the dose/pulse. Instead of multiple pulsing, an optical multichannel analyzer (OMA) records absorption spectra at a preselected time after a single pulse. The technique is based on spectrographic resolution of analyzing light and a diode array instead of a monochromator and photomultiplier as in kinetic spectroscopy. Acid–base properties are determined from spectral changes with pH. Redox properties are determined from the interactions of free radicals with oxidants and reductants.