Mössbauer Studies of Iron Organometallic Complexes. IV. Sign of the Electric-Field Gradient in Ferrocene

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Abstract
The quadrupole splitting of 57Fe Mössbauer spectra gives the magnitude, but not the sign, of the electric‐field gradient. The sign can be determined by magnetically perturbing the energy levels, such that one line splits into a triplet and the other line splits into a doublet. A first‐order perturbation treatment for the axially symmetric electric‐field gradient case is given for powdered samples. The method is applied to ferrocene, which has been the subject of many theoretical papers. A crystal‐field treatment predicts a positive efg, and molecular orbital treatments predict negative efg's. At 40 kG applied, the two lines split clearly into a doublet and a triplet. The result agrees with the MO treatment. This also explains the essential vanishing of the efg in ferrocinium compounds.

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