VARIABLE-TEMPERATURE MAGNETIC CIRCULAR-DICHROISM

A magnetic circular dichroism (MCD) spectrum is a measurement of the difference between the absorption of left and right circularly polarized light as a function of the wavelength of the measuring beam when a sample is placed in a magnetic field applied parallel or antiparallel to the direction of propagation of the light beam. There are three possible consequences to the application of a magnetic field—namely, Zeeman splitting of ground and/or excited degenerate states, field-induced mixing of states, and a change in the population of molecules over the Zeeman sublevels of a paramagnetic ground state. These give rise to contributions to the intensity of an MCD spectrum called, respectively, the A-term, the B-term, and the C-term. This chapter describes in detail for the first time the methodology used in the Norwich laboratory (University of East Anglia), which has become that almost universally employed, for the measurement of MCD spectra in the low-temperature and high-field regions. The analysis of magnetization curves is discussed and examples given briefly of the spectra of some of the main classes of transition metal centers. © 1993, Academic Press, Inc.