ESR spectra of AsF2?6 and SbF2?6

ESR spectra observed in γ-irradiated CsAsF₆ and CsSbF₆ matrices have been assigned to the free radicals AsF^2?₆ and SbF^2?₆ respectively. The large, isotropic central-atom hyperfine interactions and isotropic g-values of these species suggest that they possess ²A_tg ground-states in O_h symmetry. The contribution to the semi-occupied orbital of the central-atom valence s atomic orbital is ≈ 0.6, greater than in the halogen hexafluorides (≈0.4) and the chalcogen hexafluoride anions (≈ 0.5). Variation of the central-atom hyperfine interaction with temperature is interpreted in terms of a second-order Jahn-Teller effect involving a low-lying ²T_1u excited state.