Electron spin resonance detection of oscillating peroxy radical concentration in the cumene—anthraquinone system

Kinetic electron spin resonance spectroscopy has been applied in order to follow the variation in peroxy radical concentration in the cumene—anthraquinone system in the presence of oxygen and during UV irradiation. A periodic variation in concentration was observed, which can be caused either by hydrodynamic convections or by diffusion-controlled photochemical oscillations. For the latter case, a model was suggested in which the anthraquinone regeneration, controlled by the local oxygen concentration, can serve as a feedback mechanism, and the oscillations can be maintained by concentration gradients between the irradiated and the dark zones and by the different diffusion rates of oxygen and anthraquinone.