The diffusion of molecular hydrogen adsorbed in zeolite 13X at high coverag
e's has been studied by quasi-elastic neutron scattering Sor temperatures r
anging from 0 to 60 K, No diffusive morion was observed, within instrumenta
l resolution, at temperatures below 20 K, well above the bulk melting point
of H-2, in contrast to recent NMR studies. The diffusive motion of the ads
orbed H-2 could be described by a liquid like jump diffusion model above 35
K. The diffusion coefficient demonstrates an Arrhenius behavior. D = D-0 e
xp(E/kT), with D-0 = 1.2 x 10(-8) m(2)/s and an activation energy of E = 62
K. The inelastic scattering spectrum has also been studied. The scattering
consisted of several peaks superimposed on a broad background extending fr
om 1 meV to above 100 meV mid is consistent with rotational transitions for
a hindered rotor in a strong orientational potential with a broad distribu
tion of barrier heights.