Angular distribution of desorbing/permeating deuterium from modified Pd(1 1 1) surfaces

The angular distribution of desorbing deuterium molecules was investigated for the clean Pd(1 1 1) surface and for modified Pd(1 1 1) surfaces, either pre-covered with 0.2 ML potassium or with an ultra-thin V₂O₃ surface oxide. The palladium sample was part of a permeation source and the angular distribution was measured by lateral displacement of the sample in front of a differentially pumped flux detector. For the clean surface at 523 K, the angular distribution is close to a cosine distribution, but changes to a cos^1.9Θ distribution at 700 K. Potassium on the surface alters the angular distribution to a cos³Θ function at 523 K. The ultra-thin vanadium oxide layer on the Pd(1 1 1) surface has no significant influence on the angular distribution of deuterium desorption. The experimental results were compared with existing data of the energy dependent sticking coefficient and the energy distribution of the desorption flux as measured by time-of-flight spectroscopy. This made it possible to get information on the applicability of detailed balance and normal energy scaling.