Diffusion of ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and ${\mathrm{T}}_2$ in Single-Crystal Ni and Cu

Diffusion coefficients have been obtained for ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and ${\mathrm{T}}_2$ as a function of temperature in both Cu and Ni. The absolute-rate-theory formalism as proposed by Vineyard provides an adequate explanation of the results if quantum corrections and anharmonic effects are taken into consideration. The Ni results are especially affected by the failure of the harmonic approximation that apparently holds for Cu.