Temperature dependence of O –3 electron paramagnetic resonance signals in KCl

Abstract

An ozonide molecular ion O^–₃ has been detected by EPR spectroscopy in KCl single crystals doped with 2% KNO₃ in the melt and X-irradiated at room temperature. The temperature dependence of the O^–₃ EPR signals was investigated from 10–60 K and a gradual transition from monoclinic to orthorhombic g-tensor symmetry was found. An unexpectedly strong variation of two principal g values, one corresponding to the direction perpendicular to the molecular plane, the other with the axis connecting the two outer oxygens, was observed. These results are discussed in relation to the possible allocation of the O^–₃ to a mono- or a tri-vacancy site. The latter model has been well established by other authors for S^–₃ and Se^–₃ defects in several alkali-imetal halides. Other defects with an electronic structure comparable with that of O^–₃, for instance SO^–₂ and SeO^–₂, are believed to replace only one halide ion.