EVIDENCE FOR POLYICOSAHEDRAL STRUCTURE IN AMMONIATED IRON, COBALT, AND NICKEL CLUSTERS

Experimental evidence is presented that small (19- to 34-atom) clusters of iron, cobalt, and nickel tend to adopt polyicosahedral structure when saturated with ammonia. Clusters in the polyicosahedral series (having 19, 23, 26, 29, 32, and 34 atoms) often saturate with 12 NH3 molecules, the expected number for polyicosahedral structure. Other clusters in this size range, which do not have an obvious number of NH3 binding sites, generally do not show a clear saturation. Adsorbate-induced structural changes are also seen, and suggest that for larger clusters in the series there is a transformation to an alternate structure that binds more than 12 NH3 molecules.