Reaction yield-detected magnetic resonance RYDMAR

In the last few years, pulsed EPR or electron spin echo (ESE) and reaction yield detected magnetic resonance (RYDMAR) techniques have been added to the arsenal of EPR techniques applied in photosynthesis. ESE combines high temporal resolution (currently 100 ns) with sensitivity to broad EPR signals, and it allows rapid and accurate determination of the spin-lattice and spin-spin relaxation times. 

In RYDMAR (reviewed in Refs. R15 and R16) magnetic resonance is detected by monitoring the yield of a reaction product in the presence of microwaves resonant with the difference in energy between the levels of a coupled radical pair (which for two 5 = radicals has 1 singlet (5 = 0) and 3 triplet (5 = 1) energy levels). The yield of recombination and product formation is dependent on the relative population of the four levels, which is altered by microwave-induced transitions. 

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