Theory of Transition Ion Complexes

It is suggested that the observed lowering of the spin-orbit parameters in transition-ion complexes is caused by a screening effect which expands the $3d$ wave functions. Evidence in support of this suggestion is given by neutron diffraction form-factor measurements on ${\mathrm{Mn}}^{++}$ salts. The theory of the transferred hyperfine interaction between the electron spin of ${\mathrm{Mn}}^{++}$ and surrounding ${\mathrm{F}}^{19}$ nuclei is discussed, and the complications introduced into the theory when dealing with other ions are described. The theory is found to be unsatisfactory because it is not possible to treat the interaction via the $1s$ orbitals of ${\mathrm{F}}^{-}$ with sufficient accuracy.