ABSTRACT
Saturation-recovery EPR and saturation-recovery ELDOR monitor recovery of the EPR signal after applying a saturating microwave pulse. The recoveries are multiexponential; contributions from the various transition pathways are determined by rate equations for population differences between the various spin energy levels. Long-pulse saturation recovery selectively enhances exponential components corresponding to spin–lattice relaxation; short-pulse saturation recovery enhances contributions from spin diffusion, e.g., by nuclear relaxation and exchange processes. Long-pulse SR-EPR is determined by the mean electron spin–lattice relaxation and cross-relaxation rates and does not depend on the nitroxide hyperfine state. Short-pulse SR-ELDOR specifically resolves the nitrogen spin–lattice relaxation rate. A valuable summary is given in the concluding section of this chapter.
