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  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.
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