Paramagnetic Resonance of theVFCenter in CaF2

Abstract

Natural Ca${\mathrm{F}}_2$ crystals subjected to x rays at 77°K and then warmed to a temperature above 138°K contain $V_F$ centers. The electronic structure of this electron-deficient center has been investigated by electron paramagnetic resonance. The parameters of the appropriate spin Hamiltonian have been determined. The center appears to consist of an $\mathrm{F}_2^{}{}_{}{}^{-}$ molecule ion associated with a ${\mathrm{Ca}}^{++}$ vacancy.