Dynamic polarization in fluorocarbons: Effect of scalar correlation time

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Abstract
Multi-field nuclear-electron double resonance experiments with octafluoronaphthalene (OFN) solutions containing organic free radicals have led to the conclusion that independent fluorine scalar and dipolar correlation times are necessary to characterize these systems. Scalar correlation times were longer than dipolar times for systems with strong scalar coupling and shorter than dipolar times for systems with weak scalar coupling. This trend may be associated with the availability of the odd electron at the radical edge in conjunction with the ability of particular radical-solvent pairs to form transient complexes. Further, it signifies that a large part of the variation in F signal enhancement arises from changes in scalar correlation time. Largest observed F enhancements were + 390 for OFN with 2,3,5,6-tetrachlorosemiquinone in acetone at 1 gauss and + 435 for OFN with 2,4,6-triphenyl pyrylyl in acetone at 74 gauss.