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 determined. For O 2, 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 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 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 D 2 and substanitially lower for N 2 (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.