An electron-nuclear double-resonance (ENDOR) study of the self-trapped hole in LiF is reported. The results agree with the accepted model, i.e., the hole is shared by two halide-ion lattice sites in the form of a negatively charged diatomic halide molecule ($\mathrm{F}_2^{}{}_{}{}^{-}$ in this study). The variations in the ENDOR spectra for different ESR lines is investigated theoretically and experimentally. The observation of negative-contact hyperfine constants for most ENDOR nuclei is explained by exchange polarization of the "closed-shell" molecular orbitals.

• Received 18 March 1968

DOI:https://doi.org/10.1103/PhysRev.175.395