TEMPERATURE-DEPENDENCE OF O3- ELECTRON-PARAMAGNETIC-RESONANCE SIGNALSIN KCL

An ozonide molecular ion O3- 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 O3- EPR signals w as investigated from 10-60 K and a gradual transition from monoclinic to orthorhombic g-tensor symmetry was found. An unexpectedly strong va riation of two principal g values, one corresponding to the direction perpendicular to the molecular plane the other with the axis connectin g the two outer oxygens, was observed. These results are discussed in relation to the possible allocation of the O3- to a mono- or a tri-vac ancy site. The latter model has been well established by other authors for S3- and Se3- defects in several alkali-metal halides. Other defec ts with an electronic structure comparable with that of O3-, for insta nce SO2- and SeO2- , are believed to replace only one halide ion.