Theoretical studies of the spin Hamiltonian parameters for Cr+ in NaX (X = F, Cl, Br)

The spin Hamiltonian parameters (g factor, the hyperfine structure constant and the superhyperfine parameters) for Cr+ in NaX (X = F, Cl and Br) are theoretically studied using the perturbation formulas of these parameters for a 3d5 ion in octahedra. In the calculations, both the contributions from the crystal-field and the metal to ligand charge transfer mechanisms are taken into account for the g factor and the hyperfine structure constant based on the cluster approach in a uniform way. The calculation results show good agreement with the observed values. The charge transfer contribution to the g-shift Δg (≈g − gs, where gs ≈ 2.0023 is the spin-only value) is the same (negative) in sign and much larger in magnitude as compared with the crystal-field one. Similarly, the charge transfer contribution to the hyperfine structure constant shows the same sign and about 10% of the crystal-field one. The unpaired spin densities of the halogen ns, npσ and npπ orbitals are uniformly obtained from the quantitative relationships with the relevant molecular orbital coefficients, which are superior to the previous treatments of fitting the experimental superhyperfine parameters.