Magnetic Field Effects: MARY, MIMS and MODS*

Abstract

The principles and methodology of magnetic field effects (MFE) on the yield of photosynthetic reactions are briefly reviewed. Two basically different mechanisms are described: the MFE driven by photochemical radical pair production and subsequent spin-selective recombination (Radical Pair Mechanism, RPM), and the MFE produced by the magnetic-field induced mixing of the three sublevels of a molecular triplet state (Magnetic field Induced Mixing of Sublevels, MIMS). A number of experimental methods for measuring so-called MARY (MAgnetic field effect on the Reaction Yield) curves are described. It is shown that the MFE is a powerful tool for measuring highly accurate Triplet-minus-Singlet absorbance difference spectra (Magneto-Optical Difference Spectroscopy, MODS). A number of recent applications of the MFE in the study of photosynthetic reactions is discussed, comprising also an investigation of Optically-Detected Magnetic Resonance (ODMR) in low magnetic field, which suggests that st significant spin-orbit coupling in the triplet state of the primary electron donor leads to level anti-crossing.