Electron-Nuclear Double-Resonance Spectrum of theVKCenter in Sodium Fluoride

The electron-nuclear double-resonance (ENDOR) spectrum of the $V_K$ center in NaF was studied for each of the ESR lines, and the spectra for seven sets of neighboring nuclei were identified. The angular dependences for six of these spectra can be fitted with a spin Hamiltonian, thereby yielding the magnetic hyperfine constants and, in the case of the nearest sodium set, the quadrupole hyperfine constants. The observed differences between the ENDOR spectra for each of the ESR lines have been derived by diagonalizing the spin Hamiltonian consisting of both the ESR and ENDOR terms.