ESR studies of radical pairs of galvinoxyl radical in corresponding phenol matrix

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Abstract
ESR studies have been carried out on powder samples of galvinoxyl radical doped in its diamagnetic corresponding phenol matrix, which has the same crystal structure with that of galvinoxyl. The existence of a radical pair of the galvinoxyl has been confirmed by the observation of the ESR zero‐field splitting and half‐field resonance of its powder sample containing 0.3%–6.0% galvinoxyl in the phenol matrix. The zero‐field splitting parameters ‖D‖ and ‖E‖ have been determined to be 81.4±0.3 and 16.0±0.3 G, respectively, being independent on radical concentration. The D and E parameters were calculated for the four kinds of radical pairs existing in the crystal, based on the molecular structure and packing in crystalline galvinoxyl investigated by D. E. Williams. The calculations were performed, using (i) point‐charge, (ii) half‐charge, and (iii) point‐spin approximations, and the obtained results were compared to each other. Consequently, the observed radical pair of galvinoxyl was attributed to a nearest‐neighbor radical pair.