  Au nanoclusters grown on SiO$_2$ by physical vapor deposition are exposed to
Br$_2$ and then measured with 1.5 keV Na$^+$ low energy ion scattering. It is
found that the clusters are able to dissociate the molecules which then adsorb
as individual Br atoms, but Br$_2$ does not stick to the bare substrate nor to
bulk Au. Adsorption is the first step in any surface chemical reaction, and
this result shows how nanoclusters can induce adsorption of species that
otherwise do not stick. Results from the literature indicate that catalysis
involving nanoclusters occurs at the edges and that the edge atoms are
positively charged. This information in conjunction with the ion scattering
results lead to the conclusion that the Br adatoms are negatively charged and
ionically bonded at the edges of the clusters. Br$_2$ is also a known catalytic
poison and this work shows how its adsorption blocks sites that would otherwise
be involved in nanocatalysis.
