RHODIUM-CLUSTER REACTIVITY: STICKING PROBABILITIES OF SOME DIATOMIC MOLECULES

The reactivity of neutral rhodium clusters towards D2, N2, O2, CO, and NO has been investigated and the absolute sticking probability (S) of the first molecule on Rh10–Rh50 (Rh10–Rh35 for D2) was determined. For O2, the absolute sticking probability of the second molecule was measured. The reactions were made under single-collision-like conditions where the clusters make only one or a few collisions with reactive gas molecules. All molecules but N2 react with a high sticking probability on most cluster sizes. N2 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 O2 and NO on Rhn looked almost the same, monotonically increasing from 0.2/0.4 at n=10 to 0.8/0.9 at n=25, and the high S also remains for larger clusters. The sticking probability of CO shows small variations around S=0.6 over the entire size range. The sticking probability is somewhat lower for D2 and substanitially lower for N2 (also on cool clusters), and these two molecules display the most distinct variations in S as a function of cluster size, often with coinciding maxima and minima.