Spin-orbit splitting quenching

The chapter contains a detailed description of two methods of determining the JT energy (1) the spin-orbit splitting quenching (the Ham effect) and (2) analysis of the potential energy surfaces in the excited electronic state. 

The present chapter was devoted to the detailed consideration of the dynamic JT effect in the orbital triplet states for the 3d ions in a cubic crystal field, which included analysis of the spin-orbit splitting quenching (Ham effect) and geometry of the excited states (deformation of the equilibrium ligands configuration and cross-section of the potential energy surfaces). All necessary equations involved into such an analysis were given and explained. Theoretical description has been supported by... 

In describing the magneto-optical properties one has to take account of the spin-orbit splitting, which was not included in the band-structure calculations of de Groot et al. These authors note that no orbital quenching occurs at the F point in the Brillouin zone so that here one may expect the spin-orbit interaction to be a maximum. It follows from the magneto-optical spectra that the onset of the Kerr peak at about 2 eV is located near 1 eV (see fig. 37). From these considerations it follows that the transition responsible for the large Kerr intensity involves initial electron states located rather close to the top of the valence band (at F in the lower... 

At the moment the number of true four-component molecular EFG calculations is still rather limited due to the considerable computational effort especially in the post-DHF steps. Just five years ago Pj kko expressed the need for fully relativistic benchmark calculations in order to abandon perturbative corrections for considerable relativistic effects and to establish reference results. Furthermore spin-orbit effects can cause an EFG e.g. in atoms with Z > 0 and half-filled shells where according to nonrelativistic theory the EFG should vanish. This is the case for e.g. a system leading to a Pij2P f2 spin-orbit-split configuration. Also in closed-shell molecules with heavy halogen nuclei the spin-orbit effect is not completely quenched [88]. 

For molecules such as these, the spin-orbit effect is essentially quenched in the molecule, because to exist it must form a strong bond, and the spin-orbit splitting is not so large that the quenching cannot be achieved. This is obvious for light atoms such as C and Si, but even Pb(C2H5)4 has four equivalent sp hybridized bonds. We can... 

Moreover, the state is in principle Jahn-Teller unstable, and any such distortion can lead to partial quenching of spin-orbit splittings [28]. 

However, the spin of one electron can act on that of the other, and, if orbital motion is not quenched, this also applies to spin-orbital interactions, and this may split the ms = 0 level from the 1 levels, as, for example, in Fig. 156. This has the effect of splitting the absorption spectrum into a doublet as indicated in Fig. 156. 

The first-order JT effect is important in complexes of transition metal cations that contain nonuniformly filled degenerate orbitals, if the mechanism is not quenched by spin-orbit (Russell-Saunders) coupling. Thus, the JT effect can be expected with octahedrally coordinated and high spin d cations, and tetrahedrally coordinated and d cations. The low-spin state is not observed in tetrahedral geometry because of the small crystal field splitting. Also, spin-orbit coupling is usually the dominant effect in T states so that the JT effect is not observed with tetrahedrally coordinated d, d , d, and d ions. 

In 0, symmetry, the ground state is T g. This is split by distortions and since the three orbital states will be close in energy and connected by spin-orbit coupling, ESR signals will only be obtained at low temperatures when the spin-lattice relaxation time will be longer. When the symmetry is much reduced (e.g., G ), speetra are readily observed and g values are nearer 2 because of the quenching of the orbital angular momentum. Theory predicts that gf, < 2 and > 2 for this system (see Section IV,C,5). 

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