ELECTRON-NUCLEAR DOUBLE-RESONANCE ANALYSIS OF DIATOMIC SULFUR AND SELENIUM DEFECTS IN NABR AND NAI

In this work, a single-crystal electron-nuclear double-resonance (ENDO R) study of NaBr:S-2(-), NaI:S-2(-), and NaBr:Se; is presented. These defects have in common that the paramagnetic p lobes are parallel to t he [001] axis. For all cases, the angular variation of two sets of Na- 23 and one set of halide ENDOR transitions is investigated. The corres ponding, superhyperfine (SHF) and nuclear-quadrupole coupling tensors are determined. The two sodium interactions can be explained in terms of the nearest-neighboring Na+ ions. The halide interaction is caused by eight next-nearest-neighboring halide ions. The ENDOR results can o nly be explained in terms of a monovacancy model in which X(2)(-) (X=S , Se) ion is replacing a single halide ion on a lattice site. The near est-neighboring Na+ ions are found to be displaced outwards. The linew idth of the EPR signals can be simulated using the ENDOR SHF data.