Relativistic contributions to the amplitude of electric dipole transitionsin rare earth ions in crystals: I. Spin-orbit interaction

The third-order contributions to the amplitude of f <-> f transitions cause d by spinorbit interaction are analysed. The atomic-like properties of the perturbed functions which are the first-order corrections to the free ion r adial functions are discussed in the context of the lanthanide contraction. In addition, the values of the radial terms of the spin-orbit effective op erators evaluated for complete radial basis sets of one-electron functions of given symmetry are presented for several lanthanide ions.