Electron-Paramagnetic-Resonance Investigation of the Dynamic Jahn-Teller Effect in SrCl2:La2+

The electron-paramagnetic-resonance spectrum for Sr${\mathrm{Cl}}_2$: ${\mathrm{La}}^{2+}$ has been observed between 1.2 and 40 °K. At 1.2 °K, the dominant structure is anisotropic and is described within experimental error by second-order solutions of the effective Hamiltonian for an isolated ${}_{}{}^2{}_{}{}^{}E_g^{}{}_{}{}^{}$ state split by large random internal strains. Coexisting with the anisotropic structure at temperatures between 1.2 °K and approximately 5 °K is structure whose position is isotropic but whose intensity and linewidth are anisotropic and vary with temperature and sample treatment. This structure is shown to result from rapid direct relaxation between the strain-split vibronic states. At temperatures above approximately 6 °K, only the isotropic structure is observed.