Electron Spin Resonance of Sulfur and Selenium Radicals in Alkali Halides

Abstract

Abstract Three classes of paramagnetic radical molecules are detected in alkali halides by electron spin resonance: S 3 − and Se 3 − , SO 2 − , and SeO 2 − , and radicals formed by four equivalent sulphur or selenium atoms. The S 3 − and Se 3 − radicals occupy a trivacancy site formed by one metal and two halide vancancies. The C 2 ‐axis of the radical is orientated along a face diagonal axis of the crystal. A hyperfine interaction of the unpaired electron with three S 33 or Se 77 nuclei is observed. The unpaired electron is localized in a II ‐type molecular orbital formed by atomic p‐orbitals normal to the plane of the molecule. The S 3 − and Se 3 − centers are stable at room temperature. The electronic structure of the SO 2 − and SeO 2 − radicals is found to be analogous to that of S 3 − and Se 3 − . However, these radicals probably occupy only one halide vacancy site. Internal rotation is observed for SO 2 − and SeO 2 − , resulting in isotropic ESR‐spectra at elevated temperatures. Radicals formed by four equivalent sulphur or selenium atoms are detected in X‐irradiated chalcogen‐doped alkali halide crystals.