DIPOLAR RELAXATION ENHANCEMENT IN INHOMOGENEOUS EPR LINES WITH PARTIAL EXCITATION - AN APPLICATION TO PLANT PHOTOSYSTEM-II

The theory of dipolar relaxation enhancement is extended for incompletely excited, randomly oriented anisotroiric electron spin systems with arbitrary spin quantum numbers. Numerical calculations are presented of the spin-lattice relaxation in such systems. The relaxation is found to be generally dependent on the field position in the EPR line and to be nonexponential. Anisotropic hyperfine interactions of magnitude comparable to the g anisotropy reduce the field position dependence of the relaxation as well as the dependence of the EPR signal intensity on the magnitude of the dipolar broadening. The nonexponentiality of the experimental spin-lattice relaxation curves measured previously for plant photosynthetic material can be well explained with the theoretical model. © 1991.