Methane activation by nickel cluster cations, Nin+ (n=2-16):: Reaction mechanisms and thermochemistry of cluster-CHx (x=0-3) complexes

The kinetic energy dependences of the reactions of Ni-n(+) (n=2-16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. The main products are hydride formation NinD+, dehydrogenation to form NinCD2+, and double dehydrogenation yielding NinC+. These primary products decompose at higher energies to form NinCD+, Nin-1D+, Nin-1C+, Nin-1CD+, and Nin-1CD2+. NinCD2+ (n=5-9) and Nin-1CD2+ (ngreater than or equal to4) are not observed. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for nickel cluster cations to C, CD, CD2, and CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2, and CD3 molecular fragments to nickel surfaces. (C) 2004 American Institute of Physics.