H and D atom diffusion in ice above 140K

The authors report pulsed EPR measurements on H and D atoms produced in isotopically mixed solid water by pulse radiolysis. The atoms are highly mobile, and Chemically Induced Dynamic Electron Polarization is produced in their geminate and random recombination reactions. T2 measurements have been made over the temperature range 140K to 270K by the standard 2-pulse spin echo method. The temperature and isotope dependence of T2 is fully consistent with electron-nuclear dipole relaxation modulated by the atom diffusion through the ice lattice. Surprisingly, the D atom diffusion is faster than H diffusion above ca. 200K. This is readily explained with transition state theory in terms of motion through a constricting bottleneck