ELECTRON-PARAMAGNETIC-RESONANCE SPECTRUM OF RADICAL PAIRS IN ULTRAVIOLET-IRRADIATED (NH4)2S2O8 SINGLE-CRYSTALS

Irradiation of (NH4)2S2O8 single crystals with ultraviolet (UV) light produces two kinds of radical pair, I and II. Radical pair I is stable at room temperature, and can be produced via UV irradiation at room t emperature. The electron paramagnetic resonance (EPR) spectrum exhibit ed by radical pair I is similar to that of SO5- pairs in UV irradiated K2S2O8 crystals observed previously, and can be identified similarly. Radical pair II can be produced by UV irradiation and detected by EPR only at low temperatures. Radical pair II, which could be identified as SO4- pairs, exhibits a limited lifetime at room temperature. A rigo rous method has been developed for analysing the EPR spectra exhibited by these radical pairs.