THE QUANTUM DYNAMICS OF HYDROGEN AND DEUTERIUM ON THE PD(111) SURFACE- A PATH-INTEGRAL TRANSITION-STATE THEORY STUDY

The surface diffusion constant for hydrogen and deuterium on the palla dium (111) surface is calculated using quantum mechanical transition s tate theory. The rate constants for diffusion into the subsurface laye r are also calculated. Quantum effects are seen to be most important f or the surface/subsurface transition and cause an inverse isotope effe ct in which the rate for deuterium is greater than the rate for hydrog en. The results of ground and excited state wave function calculations show localized hydrogenic states, despite large zero point energies, and that the preferred binding site can vary with isotope between surf ace and subsurface sites. In addition, estimates of the tunneling rate between the surface and subsurface are in qualitative agreement with the low temperature transition state results.