NICKEL GROUP CLUSTER ANION REACTIONS WITH CARBON-MONOXIDE - RATE COEFFICIENTS AND CHEMISORPTION EFFICIENCY

Reactions of Ni(n)-(n = 3 - 10), Pd(n)-(n = 3 - 8), and Pt(n)-(n = 3 - 7) with CO are studied in a flow tube reactor. Bimolecular rate coeff icients are measured for the association reaction of CO adsorbing on t he cluster surface. The rate coefficients range from about 10% of the collision rate for the trimer anions to near the collision rate for cl usters larger than four atoms. The maximum number of CO molecules that bind to each cluster is determined. Whereas the saturation limits for nickel are typical for an 18 electron transition metal, the limits fo r platinum are lower, reflecting the electron deficient structures obs erved in condensed phase chemistry. The CO saturated palladium cluster s represent the first examples of saturated binary palladium carbonyl compounds. Comparisons are made to similar studies on metal cation and neutral clusters and also to surface scattering studies of nickel gro up metals.