Bidirectional CO₂ desorption in steady-state CO oxidation on Rh(110)

The angular and velocity distributions of desorbing product CO₂ were studied in steady-state CO oxidation on Rh(110) by means of cross-correlation time-of-flight techniques and low-energy electron diffraction. In the limited CO pressure range in the active region, where the reaction was fairly order in CO, the angular distribution in the plane including the [001] direction abruptly changed from a normally directed form into bidirectional lobes collimated at ±24° from the surface normal. At the same time, the CO₂ productivity was enhanced, and the (1 × 2) LEED pattern due to the missing-row structure was observed. The translational temperature of desorbing CO₂ was maximized at these collimation angles. The metastable (1 × 2) missing-row structure was proposed to be responsible for this CO₂ formation. However, in the inhibited region, where CO retarded the reaction, desorbing CO₂ was thermalized to the surface temperature.