FTMS studies of sputtered metal cluster ions. (II) The chemistry of Nin+ with C2H4 and CH4 at long timescales

Article abstract of DOI:10.1002/bbpc.19890931203

Nickel cluster cations, generated in an external source by sputtering with 20 keV Xe⁺ were transferred to the ICR cell of a Fourier transform mass spectrometer (FTMS), collisionally cooled, and trapped for long time periods. During storage, the chemistry of Ni_n⁺ was studied with ethylene and methane in the range n = 1 ... 20. Rather than undergoing adsorption as an intact unit, C₂H₄ was dehydrogenated in the 1.2-position to yield HCCH adducts Ni_n(C₂H₂)_m⁺ with a dramatic size-specificity: Whereas Ni_n⁺ ions proved absolutely inert for n = 1, 3, 4, they were found highly reactive from n = 5 on. Cyclotroning in the presence of C₂H₄ for up to 40 s, Ni₅⁺ was found to add on a maximum of nine C₂H₂ ligands. A second 'hidden' size-specific effect was discovered between n = 11 and n = 12, where dehydrogenation intensifies to yield Ni_nC₆⁺ as final products. These are being discussed in terms of close-packed lattice structures. Finally, the threshold for methane activation by Ni₅⁺ leading to Ni₅C⁺ was determined to be 2.0 ± 0.5 eV.