Reactivity of Fe n , Co n , and Cu n Clusters with O 2 and D 2 Studied at Single-Collision Conditions

This paper describes a method to study the reactivity of neutral clusters at single-collision-like conditions, which enables the determination of absolute numbers for the reaction probability (S) in a collision. A beam of clusters is produced in a laser vaporization source and skimmed and passes a cell with reactive gas, in which the clusters experience one or a few collisions with the gas molecules. The reaction products are detected with laser ionization and mass spectrometry. The depletion of pure clusters and the appearance of products are evaluated with a statistical model providing S for the first, second, etc., molecule adsorbed. The O2 and D2 reactivity of Fen, Con, and Cun has been investigated for clusters in the approximate size range 10−60 atoms. The oxidation of transition metal clusters, here exemplified by Con and Fen, shows a simple S vs n dependence, where S increases almost monotonically as n increases from 10 to 20, while for larger n, S remains high and almost constant; S ≈ 0.7 for bot...