Unstable intermediates. Part LXXVI. An electron spin resonance study of radiation damage in persulphate crystals. Interconversion of S2O8– and SO5– radicals induced by light and heat

Abstract

Exposure of various persulphate crystals to γ-rays from a ⁶⁰Co source gave two distinct radicals. That characterised by single lines (or doublets), had g₁= 2·0318, g₂= 2·0090, and g₃= 2·0037. The tensor is very close to that for the peroxyl-radical O₃SO·O^–, previously identified in u.v.-irradiated K₂S₂O₈. The doublets are shown to be associated with these peroxyl-radicals, trapped in pairs.

The second radical had g₁= 2·0142, g₂= 2·0047, and g₃= 2·0034, and a nearly isotropic coupling to ³³S with a_iso=±3·5 G. This species is identified either as SO₄^– or, more probably, as S₂O₈^–. An optical absorption in the 590 nm region, shown to be associated with this species, is readily bleached by visible light, the radical being converted into O₃SO·O^– in the non-paired form. This is reconverted almost quantitatively into the S₂O₈^–(SO₄^–) species on warming.

A possible mechanism for the radiolytic, photolytic, and thermal processes is outlined.