Hot-atom mechanism and reaction sites in photoinduced carbon monoxide oxidation on a stepped platinum (113) surface

Abstract

Angular and velocity distributions of product CO2 were measured in CO oxidation photoinduced by 193 nm laser pulses of 16 ns duration on a stepped Pt(113) surface. At low oxygen and CO coverages, the CO2 desorption was collimated at ±23° from the surface normal in a plane along step edges. CO2 is formed by the collision between CO on an atop site and translationally hot oxygen atoms emitted along the axes of oxygen molecules that lie along the step edge, resulting in declined desorption due to momentum transfer from the hot atoms. With increasing oxygen coverage, new components collimating at the (111) terrace and (100) step normal became major, while an increase in the CO coverage enhanced the CO2 desorption collimated in the normal direction. It is likely that at high coverage the reaction sites extend to (111) and (100) microfacets and also to surface troughs, yielding the above three components. The translational temperature of product CO2 was often maximized at around angles where the CO2 desorption is collimated.