The reactions of methanol on a size-selected nickel cluster ion, Ni n + (n = 3−11), were investigated at collision energies less than 1.0 eV in a beam-gas geometry. Dominant reactions were methanol chemisorption, demethanation, and carbide formation. The absolute cross sections of these different reactions were measured and found to change dramatically with the cluster size; the demethanation proceeds preferentially on Ni4 +, the carbide formation on Ni7,8 +, and the chemisorption on Ni6 +. A kinematic model explains the size-dependent characteristics that the chemisorption proceeds efficiently if the barrier height between the physisorbed and the chemisorbed states is low, and the demethanation and the carbide formation proceed otherwise. The rate of the carbide formation depends sensitively on an Ni−Ni distance of Ni n + so that it proceeds only on Ni7,8 +.

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Reactions of size-selected platinum cluster ions, Pt n + (n ) 1-5), with small hydrocarbon molecules (CH 4 , C 2 H 6 , C 2 H 4 , and C 2 H 2 ) were studied in a beam-gas cell geometry at collision energies less than 1 eV employing a tandem mass spectrometer. It was found that dehydrogenation of the hydrocarbon molecules proceeds exclusively on Pt n + and the absolute cross sections of the reactions depend critically on the cluster size, n, and the collision energy. The size-and the collision energy-dependent cross sections are successfully explained in an RRK framework.