Magnetic Circular Dichroism

Magnetic circular dichroism (MCD) is the differential absorption of left and right circularly polarized light induced by an externally applied magnetic field. MCD is one of the several forms of “higher order” spectroscopy that can augment the information provided by the measurement of the absorption of a sample using unpolarized electromagnetic radiation. The additional information provided by MCD can aid in resolving complex absorption spectra. The most sophisticated applications of MCD involve the extraction of properties of the system under study by comparison of experimental spectral parameters with theoretical models. Because of the cost and difficulty of operation of advanced CD spectrometers and superconducting magnets, MCD has developed as a field dominated by a relatively small number of specialists. The extension of MCD technology into the X-ray domain may continue this trend, as a “beam line” (experimental station) suitable for MCD spectroscopy may cost several million dollars—exclusive of the cost of the synchrotron itself.