EPR Of the SeO₄^3-, SeO₃^-, SeO₂^- and NH₃⁺ radicals in ultraviolet-irradiated crystals of ammonium compounds

Oxyradicals of selenium, such as the SeO₄^3-, SeO₄^-, SeO₃^- and SeO₂^- are conventionally produced via γ- or X-irradiation. The same is also true of the NH₃⁺ radical. We report for the first time EPR observations of these radicals produced by ultraviolet (u.v.)-irradiation in some ammonium compounds. We have investigated u.v.-irradiated crystals of (NH₄)₂SO₄, LiNH₄SO₄, (NH₄)₃H(SeO₄)₂ and NH₄H₂PO₄. The NH₃⁺ radical has been detected by EPR in u.v.-irradiated (NH₄)₂SO₄ and LiNH₄SO₄ crystals. The NH₃⁺ radical is produced at the first stage of the u.v. photo-dissociation of the NH₄⁺ ion in solids. The oxyradicals of selenium detected by EPR in some ammonium compounds can be regarded as the product of an u.v. photo-redox reaction between the NH₄⁺ ion and the SeO₄^2- ion.