Anisotropic velocity distribution of desorbing product in carbon monoxide oxidation on palladium (110)

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Abstract
Significant anisotropy was found in the velocity distributions of desorbing product CO2 from a Pd(110) surface. The velocity distributions were determined by a cross‐correlation time‐of‐flight technique combined with angle‐resolved thermal desorption. Heating the coadlayer of CO and oxygen produces five peaks in the CO2 formation spectrum; P 1– (around 420 K), P 2– (∼370 K), P 3– (∼300 K), P 4– (∼230 K), and P 5–CO2 (∼170 K). The translational temperature of each CO2 is much higher than the corresponding surface temperature, and increases in the sequence of P 1– <P 2– <P 3– <P 4– <P 5–CO2. It decreases rapidly with an increase in the desorption angle perpendicular to the surface trough and more slowly parallel to it. This anisotropy is correlated to the reaction site symmetry.