Electron spin resonance of irradiated NaH3(SeO3)2 and NaD3(SeO3)2

Abstract The electron spin resonance spectra of γ-irradiated NaH 3 (SeO 3 ) 2 and NaD 3 (SeO 3 ) 2 single crystals have been investigated, and the principal stable damage centres could be identified as SeO 2 − . The spectra consist of a central part, due to those SeO 2 − groups which are composed of spinless isotopes of Se and of a number of satellites due to hyperfine interaction with Se 77 . At room temperature four physically non-equivalent free radicals have been found in the unit cell of non-polar NaH 3 (SeO 3 ) 2 and NaD 3 (SeO 3 ) 2 , two of them being also chemically non-equivalent and the complete g and hyperfine coupling tensors have been determined. A tentative model of the electronic structure of the damage centre is proposed. Significant changes were found in the spectra on cooling the samples below the corresponding ferroelectric NaH 3 (SeO 3 ) 2 respectively anti-ferroelectric NaD 3 (SeO 3 ) 2 transition points, which have been explained by reversible reorientations of the SeO 2 − radicals.