Low-symmetry effects

FIGURE 5.8 Complex hyperfine patterns due to axes noncolinearity in a low-symmetry prosthetic group. The X-band spectrum is from 65Cu(II)-bicarbonate in human serum transferrin (a,b) experimental spectrum (c,e) simulation assuming axial symmetry (d, f) simulation assuming triclinic symmetry with the A-axes rotated with respect to the g-axes over 15° about the gz-axis and then 60° about the new y -axis. Traces b, e, and f are 5x blow-ups of traces a, c, d, respectively (Hagen 2006). (Reproduced by permisson of The Royal Society of Chemistry.) 

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Qualitatively, all proposals indicate a linear dependence on ml (linewidth over a hyperfine pattern increases from low to high field or vice versa cf. Figure 9.4) plus a quadratic dependence on m, (outermost lines more broadened than inner lines). Multiple potential complications are associated with the lump parameters A, B, C, notably, their frequency dependence (Froncisz and Hyde 1980), partial correlation with g-strain (Hagen 1981), and low-symmetry effects (Hagen 1982a). The bottom line quantitative description of these types of spectra has been for quite some time, and still is, awaiting maturation. 

The phenomenon of asymmetric hfs tensors was first discussed by McConnell134). Later, Kneubiihl135,136) proved the existence of asymmetric g and A tensors in paramagnetic systems with low symmetry. Evaluation of the asymmetry of A using EPR and ENDOR spectroscopy has been treated by several authors132,137 141). Recently, low-symmetry effects in EPR have been covered in a comprehensive review article by Pilbrow and Lowrey142). 

An abrupt change occurs between the cluster (r2) and the cluster (r3) as shown in Fig 4. Therefore, the dominant factor of the low-symmetry effect is the asymmetric position of the chromium ion along C,-axis as shown in Fig 1. For the cluster with cubic approximation (rS), the energies of U and Y are considerably overestimated. In the traditional analysis based on the ligand-... 

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