User:Younga2

Introduction
Magnetic circular dichroism (MCD) spectroscopy is based upon the measurement of the difference in absorption between left circularly polarized (lcp) light and right circularly polarized (rcp) light, induced in a sample by a strong magnetic field oriented parallel to the direction of light propagation. The difference absorption, or dichroism, is defined by convention as ΔA= A- - A+ where A- is lcp absorption and A+ is rcp absorption. The measured ΔA is the same as natural circular dichroism (CD) which is observed for chiral (optically active) molecules in regions of absorption. However, the origin of CD and MCD is quite different. MCD is a universal property of light absorption for all matter when placed in a magnetic field, and is due to electromagnetic interaction of the external field with electronic charge within the sample, no matter how it is distributed. In either case, however, the quantity ΔA is analogous to conventional light absorption, where A=(A- + A+)/2. It obeys the Beer-Lambert Law and is proportional to concentration. In addition, magnetically induced ΔA for MCD is proportional to the magnetic field B, by the equation ΔA= ΔεmclB, where Δεm is the differential molar absorptivity per Tesla of field, c is molar concentration, and l is path length in centimeters. The ΔA for MCD results from a magnetic perturbation (the Zeeman effect) of the states involved in optical transition(s) responsible for light absorption. The phenomenon is related to the Faraday effect. An important experimental consideration is that ΔA, like A, is approximately equal to zero in transparent regions of the spectrum and is not strongly affected by imperfections in optical elements that cause the rays to split, such as windows, lenses, cells, etc., that are part of spectrometers. In contrast, optical rotation can have significant magnitude in transparent regions of the spectrum. The development of MCD really began in the 1930s when a quantum mechanical theory of MOR(magnetic optical rotatory dispersion) in regions outside absorption bands was formulated. The expansion of the theory to include MCD and MOR effects in the region of absorptions, which were referred to as “anomalous dispersions,” was developed soon thereafter. There was, however, little effort made to refine MCD as a modern spectroscopic technique until the early 1960s. Since that time there have been numerous studies of MCD spectra for a very large variety of samples, including stable molecules in solutions, in isotropic solids, and in the gas phase, as well as unstable molecules entrapped in noble gas matrices. More recently, MCD has found useful application in the study of biologically important systems including metalloenzymes and proteins containing metal centers.

Example 1
First really awesome example

Example 2
Second really awesome example