Vs. Oganesyan et Aj. Thomson, Magnetic circular dichroism of symmetry and spin forbidden transitions of high-spin metal ions, J CHEM PHYS, 113(12), 2000, pp. 5003-5017
Recently we have developed a general method of analyzing magnetic circular
dichroism (MCD) spectra and magnetization curves of high-spin metal ions fo
r spin-allowed transitions [Oganesyan , J. Chem. Phys. 110, 762 (1999)]. In
the present article this approach is extended to cover the cases of spin-
and symmetry-forbidden transitions. At high ligand fields many low-energy l
igand field transitions become spin-forbidden. Extraction of information co
ntent about the electronic structure of the ground state can be obtained th
rough the analysis and correlation of the positions, signs, and intensities
of the MCD bands and magnetization curves of these transitions. The castin
g of the theory in terms of the irreducible tensor method allows full advan
tage to be taken of any symmetry elements and simplifies multielectron calc
ulations. The theory is valid over the entire range of magnetic field stren
gth and, therefore, allows the information content of spectra over the full
field and temperature range to be exploited. The method is applied to the
analysis of the recorded MCD spectra and magnetization curves of the lowest
energy spin-forbidden ligand field transitions of pseudo-tetrahedral high-
spin Fe(III), S=5/2, in the protein rubredoxin from Methanobacterium thermo
autotrophicum (strain Marburg). The predicted signs, intensities, and magne
tization curves for these transitions are in excellent agreement with exper
imental data. We also show that when the anisotropy of the ground state is
larger than the Zeeman splitting the MCD of both spin-forbidden and allowed
transitions can become comparable in magnitude. Hence caution is needed in
order to avoid the misinterpretation of experimental results. (C) 2000 Ame
rican Institute of Physics. [S0021-9606(00)01236-8].