Rotational strength transition metals

A large number of X-band ENDOR spectrometers have been discussed in the literature. Instruments operating in the less common K-19), Q-20,21 and V-22 frequency bands have also been described. Most of the ENDOR spectrometers are so-called low-power systems which produce rf fields = 0.1 mTrot (rot rotating frame). These field strengths are often sufficient to achieve nuclear saturation in transition metal complexes, i.e. to meet the condition (1.2). 

The major contribution to the rotational strength of optically active complexes of transition metals is usually the chiral arrangement of chelate rings. The additivity of the contributions to the rotational strength was demonstrated (1 ) for complexes of the type [Co(en)2(aa)] + (aa = amino acid anion). The A- and A- isomers of [Co(en)2(S-pala)] + are diastereoisomers, not enantiomers. The CD curves (Figure 1) are not mirror images. 

The optical activity in valence excitations of chiral metal complexes has been effectively treated using the model of an achiral chromophore (metal ion) in a chiral environment (ligands) and this model appears also appropriate for XAS in view of the core nature of the initial orbital state. The zero-order electric and magnetic transition moments arise from different transitions and must be mixed by some chiral environmental potential (V ). Considering the case of a lanthanide ion, and taking tihe electric dipole transitions for the Z.2,3 edge as Ip—Kj), a first-order perturbation expression for the rotational strength looks like ... 

Importantly, physical and chemical properties of nanoparticulate films are markedly different from those of the bulk materials. For example, magnetic nanoparticles can be prepared where only one magnetic domain is present, so that the rotation or alignment of the whole particle implies the rotation or alignment of the magnetic moment [53]. Semiconductor nanoparticles possess strong nonlinear optical properties due to increased oscillator strength within excitonic transitions [54-56]. Electrooptical shifts can be induced in metal particles because the surface plasmon band position depends on the free electron concentration electron injection can be used to modulate the peak position [57]. 

---