Isomer shifts and hyperfine fields in ferrous dihalides

With the use of electronic wave functions obtained from first-principles unrestricted Hartree-Fock calculations, obtained for earlier studies of ⁵⁷ᵐFe nuclear quadrupole interactions, the isomer shifts in FeCl₂ and FeBr₂ with respect to metallic iron have been evaluated and found to be in satisfactory agreement with experimental results. The hyperfine fields have also been evaluated and are found to be rather anisotropic due to the importance of dipolar contributions, the components parallel and perpendicular to the molecular axis being H_hfᵖᵃʳᵃ=-199 and -193 kG for FeCl₂ and FeBr₂ and H_hf^⊥=-474 and -464 kG, including many-body effects. It is hoped that experimental results from M\"ossbauer measurements will be available in the future to test these predictions.