Oxidation of small transition metal clusters

The initial oxidation of gas phase metal clusters is studied in a new experimental configuration. A beam of neutral metal clusters is produced in a laser vaporization source, and after skimming the beam passes a reaction cell where the clusters undergo one or a few collisions with oxygen molecules. The reaction products are detected with laser ionization and mass spectrometry. We have determined the sticking probability, S, of O2 on FeN, CoN and CuN clusters, with Nκ 10–60. FeN and CoN show a similar size dependence with low sticking probability, S < 0.2, for the smallest sizes, then increasing almost monotonically to Nκ 25, where S levels out at a constant value of 0.7 (FeN) or 1.0 (CoN). CuN shows a different size behavior with reactivity minima for clusters with closed electronic shells.