| Summary: | The EPR parameters <i>g</i> factors and the superhyperfine parameters for the tetrahedral [FeX<sub>4</sub>]<sup>-</sup> clusters in AgX (X=Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a <i>3</i>d<sup>5</sup> ion under tetrahedra by considering both the crystal-field and charge transfer contributions.The related model parameters are quantitatively determined from the cluster approach in a uniform way. The <i>g</i>-shift Δ<i>g</i> (=<i>g-g<sub>s</sub></i>, where <i>g<sub>s</sub>≈2.0023</i> is the spin only value) from the charge transfer contribution is opposite (positive) in sign and much larger in magnitude as compared with that from the crystal-field one. The importance of the charge transfer contribution increases rapidly with increasing the covalency and the spin-orbit coupling coefficient of the ligand and thus exhibits the order of AgCl < AgBr. The unpaired spin densities of the halogen ns, np<i>σ</i> and np<i>π</i> orbitals are quantitatively determined from the related molecular orbital coefficients based on the cluster approach.
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