Saturation of the Paramagnetic Resonance of aVCenter

The saturation of the paramagnetic resonance of the ${\mathrm{}\left(\mathrm{halogen}\right)\mathrm{}}_2^{-}$ complex ($V_K$ center) in the alkali halides has been studied. The saturation of the absorption signal (${\chi }^{\prime \prime }{H}_1$) versus $H_1$ is obtained over a 60-db power range for KCl, KBr, and LiF at 78°K. Portis' theory of inhomogeneous saturation has been generalized by omitting the assumption that the individual spin packet width is very much smaller than the envelope width. Methods are developed to determine independently from a given experimental saturation curve the spin-packet width $\frac{1}{T_2}$, the spin-lattice relaxation time $T_1$, and the product $T_1{T}_2$. For KCl and LiF values of $T_2$, $T_1$ and $T_1{T}_2$ are determined for the different hyperfine lines of the $V_K$ center spectrum. For KBr only the product $T_1{T}_2$ could be obtained. From the results it is concluded that the spin-packet width is not limited by $T_1$. For KCl at 78°K, $T_1\sim 7T_2$; for LiF, $T_2$ is two orders of magnitude or more less than $T_1$ and depends in a complicated manner on the external magnetic field and the angle between the $V_K$ center axis and the external field.