Editing Magnetic circular dichroism (section)

== Example on C terms ==
[[File:Aqueous Potassium Ferricyanide Magnetic Circular Dichroism.svg|thumb|upright=2|An MCD spectrum and orbital diagram for potassium ferricyanide]]
In the visible and near-ultraviolet regions, the [[Ferricyanide|hexacyanoferrate(III)]] ion ([[Iron|Fe]]([[Carbon|C]][[Nitrogen|N]])<sub>6</sub><sup>3−</sup>) exhibits three strong absorptions at 24500, 32700, and 40500&nbsp;cm<sup>−1</sup>, which have been ascribed to ligand to metal charge transfer (LMCT) transitions. They all have lower energy than the lowest-energy intense band for the Fe(II) complex Fe(CN)<sub>6</sub><sup>2−</sup> found at 46000&nbsp;cm<sup>−1</sup>.<ref>{{cite journal|author=Stephens, P. J. |journal=Inorg. Chem.|date=1965|volume=4|pages=1690–1692|doi=10.1021/ic50034a003|title=The Faraday Rotation of Allowed Transitions: Charge-Transfer Transitions in K3Fe(CN)6|issue=12}}</ref> The red shift with increasing oxidation state of the metal is characteristic of LMCT bands. Additionally, only A terms, which are temperature independent, should be involved in MCD structure for closed-shell species. 

These features can be explained as follows. The ground state of the anion is <sup>2</sup>T<sub>2g</sub>, which derives from the electronic configuration (t<sub>2g</sub>)<sup>5</sup>. So, there would be an unpaired electron in the d orbital of Fe<sup>3+</sup>
From that, the three bands can be assigned to the transitions <sup>2</sup>t<sub>2g</sub>→<sup>2</sup>t<sub>1u</sub><sup>1</sup>, <sup>2</sup>t<sub>2g</sub> →<sup>2</sup>t<sub>1u</sub><sup>2</sup>, <sup>2</sup>t<sub>2g</sub> →<sup>2</sup>t<sub>2u</sub>. Two of the excited states are of the same symmetry, and, based on the group theory, they could mix with each other so that there are no pure σ and π characters in the two t<sub>1u</sub> states, but for t<sub>2u</sub>, there would be no intermixing. The A terms are also possible from the degenerate excited states, but the studies of temperature dependence showed that the A terms are not as dependent as the C term.<ref>{{cite journal|author1=Upton, A. H. P. |author2=Williamson, B. E. |journal=J. Phys. Chem.|date= 1994|volume=98|pages=71–76|doi=10.1021/j100052a013|title=Magnetic circular dichroism and absorption spectra of hexacyanoferrate(III) in a poly(vinyl alcohol) film}}</ref>

An MCD study of Fe(CN)<sub>6</sub><sup>3−</sup> embedded in a thin [[polyvinyl alcohol]] (PVA) film revealed a temperature dependence of the C term. The room-temperature C<sub>0</sub>/D<sub>0</sub> values for the three bands in the Fe(CN)<sub>6</sub><sup>3−</sup> spectrum are 1.2, −0.6, and 0.6, respectively, and their signs (positive, negative, and positive) establish the energy ordering as <sup>2</sup>t<sub>2g</sub>→<sup>2</sup>t<sub>1u</sub><sup>2</sup><<sup>2</sup>t<sub>2g</sub>→<sup>2</sup>t<sub>2u</sub><<sup>2</sup>t<sub>2g</sub>→<sup>2</sup>t<sub>1u</sub><sup>1</sup>