EPR Identification of the Structure of theV1Color Center in KCl

Abstract

EPR spectra have been observed in KCl for a radiation-induced defect center having the same optical and thermal bleaching properties as the center responsible for the $V_1$ optical-absorption band. The spectra are interpreted as due to an interstitial ${\mathrm{Cl}}^0$, or an $H$ center, adjacent to a substitutional cation impurity, most likely ${\mathrm{Na}}^{+}$. The impurity ion is in the {100} plane containing the $H$-center bonding axis and is located nearest the midpoint of the $H$ center. The hyperfine principal axes of the two central Cl nuclei, which are coincident with their bonding axes, are inclined 2.8° and 8.8° from a $〈110〉$ direction toward the impurity ion. An analysis of motional effects on the EPR spectra leads to the following values for the activation energy for reorientation: 0.027 eV for the $H$ centers, 0.035 eV for the $V_1$ center.