The correlation between the inclination of surface reaction sites and the spatial distribution of desorbing product molecules

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1. In this project focused on the inclination of the reaction sites, the spatial distributions of desorbing product CO_2 in the CO oxidation are measured on several stepped platinum surfaces, Pt(110)(1x2)(the inclining angle of terraces : 35.2ﾟ), Ir(110)(1x2)(35.2ﾟ), Pt(112)(19.5ﾟ), Pt(335)(14.4ﾟ) and Pt(557)(9.5ﾟ), to examine how accurately the inclination is preserved in the spatial distributions. The angle has been confirmed to be preserved to about 85% in the spatial distribution. This means that the spatial distribution measurements are powerful to identify reaction sites.2. The CO_2 formation induced by heating the coadlayr of CO and oxygen on the stepped surfaces mentioned above is extended to lower temperatures, with increasing the reaction coverages, yielding several peaks in the range of 150-400 K.The spatial and velocity distributions of each peak have been separately analyzed. The translational temperature of desorbing CO_2 is maximized at the desorption angle where the flux is maximized and decreases quickly with increasing the shift of the angle. This indicates the mechanism in which the spatial distribution is sharpened, i.e., the velocity component of desorbing product is enhanced in the normal direction of the reaction sites.3. The reaction sites are extended from the terraces to steps or into surface troughs when the reactant coverages are increased. The desorption component not collimated in the terrace normal is increased at high coverages.