Influence of alkali coadsorption on hydrogen recombination at Cu(1 1 1)

The role of alkali coadsorption on the barrier to deuterium recombination and dissociation has been studied by examining the translational energy distributions of D2 formed by recombination at a cesiated Cu(1 1 1) surface. Cesium coadsorption stabilises H/D on the surface, increasing the barrier to desorption from 0.78 eV on the clean Cu(1 1 1) surface to ∼1 eV in the presence of Cs. The energy distribution of the desorbing D2 broadens substantially, recombination showing a higher energy release but also an increase in the low energy pathways available for recombination. Detailed balance predicts that an increase in the energy required for efficient dissociation on the Cs covered surface is accompanied by an enhanced probability for dissociation at low energy. This behaviour is interpreted in terms of a local reduction in the barrier to D2 recombination/dissociation near to Cs but a long range poisoning of reaction on the Cu(1 1 1) terraces, these two effects operating in opposition to each other.