Guided ion beam studies of the reactions of Fe+<i>n</i> (<i>n</i>=2–15) with D2: Cluster–deuteride bond energies as a chemical probe of cluster structures

Abstract

The kinetic energy dependencies of the reactions of Fe+n (n=2–15) with D2 are studied in a guided ion beam mass spectrometer. The only products observed are FenD+ (n=2–15) and FenD+2 (n=9–15). All reactions are observed to exhibit thresholds, except for formation of Fe9D+2. Threshold analyses of the endothermic reactions lead to binding energies for the first deuterium atom to the cluster ions as a function of cluster size. The Fe+n–D bond energies are compared to previously determined metal–metal bond energies, D0(Fe+n–Fe). The bond energies of Fe+n–D vary nonmonotonically with n, and parallel those for Fe+n–Fe except for notable differences at n=5, 8, 12, and 14. These trends are rationalized in terms of electronic and geometric structures for the Fe+n clusters. Arguments are presented to suggest that the thresholds measured for FenD+2 production correspond to barriers for chemisorbtion.