Magnetic circular dichroism is observed when a sample differentially absorbs left- and right- circularly polarized light in a magnetic field parallel to the light beam.
Notes: - The MCD signal, Δ, is calculated as \[\Delta = \frac{\alpha(\lambda)^{-}\,-\,\alpha(\lambda)^{+}}{\alpha(\lambda)^{-}\,+\,\alpha(\lambda)^{+}}\] with α(λ)- and α(λ)+ the absorption coefficients for right and left circularly polarized light, respectively. The spectra are a representation of Δ vs @W06659@. Often, Δ is recorded as a function of the applied field (up to 10 T) and the temperature.
- Phenomenon related to 'magnetically induced @O04303@ (Faraday effect)' by the 'Kramers-Kronig transformations', which connect optical refraction and absorption, i.e., MCD is observed in optically active materials at wavelengths with non-vanishing absorption. It occurs for @D01668@, @P04404@ and (@A00381@)-ferromagnetic material and has been observed from IR (@IT07399@) to X-ray regions. MCD optical transitions in molecular species arise if (i) degenerate electronic states are split in the presence of a magnetic field (first-order-@Z06739@) or (ii) states are mixed together by the applied magnetic field (second-order-@Z06739@). This may occur in the initial or the final states.
- MCD is used as a probe of paramagnetism that permits the identification of the electronic and magnetic properties of the ground states of transition metal ion centres. The @W06659@ dependence of MCD can be used also to identify and assign optical transitions from metal ion sites.
- Technique complementary to both EPR and electronic absorption spectroscopies in facilitating assignment of the ground-state spin and electronic transitions of a molecular entity.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 368 (https://doi.org/10.1351/pac200779030293)