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

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; P1– (around 420 K), P2– (∼370 K), P3– (∼300 K), P4– (∼230 K), and P5–CO2 (∼170 K). The translational temperature of each CO2 is much higher than the corresponding surface temperature, and increases in the sequence of P1– <P2– <P3– <P4– <P5–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.