RHODIUM-CLUSTER REACTIVITY - STICKING PROBABILITIES OF SOME DIATOMIC-MOLECULES

The reactivity of neutral rhodium clusters towards D-2, N-2, O-2, CO, and NO has been investigated and the absolute sticking probability (S) of the first molecule on Rh-10-Rh-50 (Rh-10-Rh-35 for D-2) was determ ined. For O-2, the absolute sticking probability of the second molecul e was measured. The reactions were made under single-collision-like co nditions where the clusters make only one or a few collisions with rea ctive gas molecules. All molecules but N-2 react with a high sticking probability on most cluster sizes. N-2 molecules adsorbed on clusters produced in a liquid-nitrogen-cooled cluster source, while cooling the cluster source did not significantly change S for the other molecules . The sticking probability of O-2 and NO on Rh-n looked almost the sam e, monotonically increasing from 0.2/0.4 at n = 10 to 0.8/0.9 at n = 2 5, and the high S also remains for larger clusters. The sticking proba bility of CO shows small variations around S = 0.6 over the entire siz e range. The sticking probability is somewhat lower for D-2 and substa nitially lower for N-2 (also on cool clusters), and these two molecule s display the most distinct variations in S as a function of cluster s ize, often with coinciding maxima and minima.