Hyperfeinstrukturuntersuchungen an wasserfreien Eisenhalogeniden mit Hilfe des Mössbauereffektes

Mössbauer effect measurements were performed with the anhydrous iron halides FeCl₂, FeBr₂ and FeI₂ at 78° K and 4 K° and with FeCl₃ at 4 °K. The quadrupole splitting, the isomer shift and the magnetic field at the nucleus were determined. From the quadrupole splitting it follows that in FeCl₂, FeBr₂ and FeI₂ the ground state is a doublet and that the singulet in these compounds is separated from it by (145±35) cm^?1, (175±35) cm^?1 and (135±35) cm^?1 respectively. The isomer shift shows the presence of strong covalence effects in all compounds. The large isomer shift in FeBr₂ cannot be fully explained. From the isomer shift and the magnetic field at the nucleus in FeCl₃ it can be concluded that the Fe⁺⁺⁺ ions has an 3d ^5,6 4s ^0,45 configuration. In FeCl₂, FeBr₂ and FeI₂ the smallness of the magnetic field can be explained by a not fully quenched orbital angular momentum of 0.6<L _z<1.