The angular distributions of desorbing products were examined in 193 nm photo-induced reactions of the O₂ + CO adlayers on stepped Pt(112) = [(s) 3(111)×(001)]. At high coverage of O₂(a) and CO(a), the product (CO₂) desorption collimated closely the (111) terrace normal, where the translational temperature was maximized to 3240 K. On the other hand, at low coverage, the CO₂ desorption collimated in highly inclined ways in the plane along the surface troughs, where the translational temperature was enhanced, confirming the hot atom mechanism. These results were compared with those in thermal CO oxidation and the origin of the collimation angle shift in the latter was discussed.