Undecomposed NH3 was found to adsorb on the top site, Figure . After a coverage of 0.5 monolayer of NH3, additional NH3 only weakly physisorb at a large distance above the surface layer. This can be seen as a saturation of the NH3 coverage, since when an ammonia molecule binds to a metal site, it will contribute with two valence electrons to the surface metals. At a 0.5 ML NH3 coverage, the number of valence electrons will form a full octet for each surface metal by forming a bond to the ammonia on half of the sites and a free electron pair on the other half.