EFFECT OF PREADSORBED OXYGEN ON THE DIRECT DISSOCIATIVE CHEMISORPTION OF ETHANE ON IR(110)

Molecular beam techniques were employed to determine the effect of preadsorbed oxygen on the direct dissociative chemisorption of ethane on Ir(110) at a surface temperature of 600 K. The direct dissociative chemisorption of ethane on Ir(110) has been investigated using translational beam energies of 12 to 30 kcal/mol, parametric in oxygen precoverage from the clean surface to the oxygen-saturated surface [1 monolayer (ML) of dissociatively adsorbed oxygen]. We observed that the probability of direct dissociative chemisorption decreases in the presence of dissociatively adsorbed oxygen. For all beam translational energies studied, an oxygen precoverage of 0.12 ML decreases the probability of direct dissociative chemisorption of ethane to approximately one-half the probability observed on clean Ir(110). For oxygen precoverages below 0.5 ML, the probability of direct dissociative chemisorption of ethane increases with increasing beam translational energy. However, for oxygen precoverages of 0.5 ML or greater, the probability of direct dissociative chemisorption is independent of beam translational energy. In the case of high 0.5 ML) oxygen precoverages, CO evolution is detected from the surface during the dissociative chemisorption of ethane, resulting in a transient enhancement of the probability of chemisorption prior to ultimate poisoning by carbon. © 1995, American Vacuum Society. All rights reserved.