Crystal charge transfer electronic transition

The electronic spectra of a variety of transition metal-bearing oxide and silicate minerals have been measured at high pressures and/or elevated temperatures. Trends for absorption bands originating from crystal field (CF), metal-metal intervalence charge transfer (IVCT) and oxygen —> metal charge transfer (OMCT) transitions are summarized in tables 9.2,9.3 and 9.4, respectively. 

The electronic spectrum of the complex consists of a combination of the spectra of the parent compounds plus one or more higher wavelength transitions, responsible for the colour. Charge transfer is promoted by a low ionization energy of the donor and high electron affinity of the acceptor. A potential barrier to charge transfer of Va = Id — Ea is predicted. The width of the barrier is related to the intermolecular distance. Since the same colour develops in the crystal and in solution a single donor-acceptor pair should be adequate to model the interaction. A simple potential box with the shape... 

Additional information has been obtained from single crystal, polarized optical and ESR spectroscopic studies924 on poplar plastocyanin, which have allowed a correlation of the electronic structure of the blue copper active site with its geometric structure. In summary, the three dominant absorption bands at 13 350, 16 490 and 17 870 cm-1 were assigned to CysS- Cu (d 2-,2 charge-transfer transitions. The methionine makes only a small contribution, due to the long Cu—S(Met) bond (2.9 A) and the poor overlap of the methionine sulfur orbitals with the dx y orbital of copper. Histidine-Cu charge transfer contributes to the weaker absorptions at 21 390 and... 

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