Transition-metal Ions. II. Electron Resonance in the Gas Phase

Abstract

All of the ions considered in Chap. 11 were those for which the ground state is orbitally nondegenerate. The deviations of the g factors from g _e are adequately described by the use of second-order perturbation theory. In Chap. 12 we encounter examples in which the crystal field does not completely remove the orbital degeneracy of the free ion. Hence, the ground state will have a net orbital angular momentum. It is not possible to treat the spin and orbital angular momenta independently; hence, the approach used in Chap. 11 is no longer applicable. Instead one must consider the effect of the spin-orbit coupling operator in terms of the total angular momentum of the ground state. Since the resulting splitting of states is usually much larger than kT, one can deal primarily with the lowest-lying state. It is essential to determine the degeneracy and eigenfunctions for this state as these determine the characteristics of the ESR spectrum. The ions in the various crystal fields to be considered in this chapter are listed in Table 12–1.