Preferential Thermal Reorientation ofVKCenters in Potassium Chloride

The thermally excited reorientation of $V_K$ centers in KCl(Pb) has been studied using both optical and electron-spin-resonance techniques. Both methods of detection show that $V_K$ centers reorient through 60° only; the probability of reorienting through 90° is effectively zero. This indicates that $V_K$ centers reorient by jumping to first-nearest-neighbor sites. Further, the thermal activation energy (0.54 eV) measured in the optical-absorption experiments, when compared with a previous value determined elsewhere for the long-range diffusion of $V_K$ centers, shows that this diffusive motion is probably by first-nearest-neighbor jumps only.