Diffusion of Methyl-Group Tunneling Energy

Dynamic nuclear polarization is observed when methyl groups in ammonium acetate at 4.2 K are converted between E and A spin-symmetry species by paramagnetic impurities whose Zeeman splitting is tuned to the methyl-group tunnel splitting. Further nuclear polarization is subsequently generated as the effect on resonant methyl groups is transferred to nonresonant ones by spin-symmetry diffusion. The time constant for the establishment of internal thermal equilibrium among the methyl groups is measured.