Reactions of Ni-38 with N-2, H-2, and CO: Cluster structure and adsorbate binding sites

The gas-phase reactions of nitrogen, hydrogen, and carbon monoxide with Ni-38 are studied as a function of reagent pressure at several reaction temperatures. Saturation coverage of the cluster is found at Ni-38(N-2)(24), Ni38H36, and Ni-38(CO)(36). These saturation levels are consistent with the metal core of the ligated cluster having the structure of a truncated octahedron in each case. An alternate fee structure derived from a 40-atom truncated tetrahedron is consistent with the nitrogen data, but not with the hydrogen or carbon monoxide results. In addition, the nitrogen uptake data indicate that the bare Ni-38 cluster also has the structure of a truncated octahedron or possibly a deformed truncated octahedron. There is no indication that Ni-38 has an icosahedral or polyicosahedral structure. The nature of the binding of the three reagents to the cluster is discussed. Evidence is presented that CO initially binds to atop sites, but following saturation of thesesites a local rearrangement to bridge sites occurs that allows an increase in coverage to the observed saturation at Ni-38(CO)(36) At high reagent pressures all three reagents cause adsorbate-induced structural changes to isomers that bind more ligands and whose structures have yet to be determined. (C) 1997 American Institute of Physics.