Paramagnetic-Resonance Spectra ofS−Trapped in Alkali Halide Crystals

An impurity identified as ${\mathrm{S}}^{-}$ has been investigated by means of paramagnetic resonance in certain alkali halide crystals. The $p$ function containing the unpaired electron points along $〈110〉$ directions in the crystal and the center has orthorhombic symmetry. A quantitative understanding of the $g$ factor and of the ${\mathrm{S}}^{33}$ hyperfine structure could be obtained. In particular it was found that three parameters are needed to describe the hyperfine splitting: an effective spin density at the sulfur nucleus and two different averages over ${\mathcal{r}}^{-3\mathrm{}}$. The values determined for these parameters were used to calculate the hyperfine splitting in other sulfur-containing centers.