REACTIONS OF COPPER GROUP CLUSTER ANIONS WITH OXYGEN AND CARBON-MONOXIDE

Reactions of copper group cluster anions, Cu-n(-) (n less than or equal to 13), Ag-n(-) (n less than or equal to 13), and Au-n(-) (n less than or equal to 7), with oxygen and carbon monoxide are investigated using a flow tube reactor instrument. The metal cluster anions are prepared in a flowing afterglow ion source with a cold cathode de discharge. Thermal effective bimolecular reaction rate coefficients are reported along with determinations of the product ions. The primary reaction channel is addition of one CO or O-2 molecule to the metal cluster anion. A dramatic even/odd alternation with cluster size n is found for the reaction rates with oxygen; even n clusters (odd valence electron) anions are more reactive than odd n clusters. In the reactions of Cu-n(-) and Au-n(-) with carbon monoxide, larger clusters (n > 4) are more reactive than small clusters, and there is no even/odd alternation in rates. Silver cluster anions are unreacted toward CO. The effective bimolecular rate coefficients are pressure dependent for the reactions Cu-n(-) + CO (n = 7-11), Au-n(-) + CO (n = 5-7), and Au-n(-) + O-2 (n = 2, 4, and 6). Lifetimes of the cluster/adsorbate complexes are estimated from termolecular rate coefficients.