H and I9F NMR spin-lattice relaxation times and dynamic nuclear polarization (DNP) enhancements have been measured at various temperatures in a magnetic field of 17 mT for solutions of six polyfluorinated benzenes containing free radicals. From the radical induced relaxation rates and DNP coupling factors, dipolar and scalar hyperfine coupling contributions have been separated. As a result, the dipolar fluorine and the total proton relaxation rates are more or less the same, and they are only controlled by the molecular motion. The scalar relaxation rates depend upon the chemical structure, but their temperature dependence is also given by the process of translational diffusion. The activation energies for molecular translation, and the scalar contact coupling intensity both increase as one goes from mono-to hexafluorobenzene. Coupling mechanisms and comparison with viscous flow and diffusion are discussed.

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