CO 2 desorption initiated by irradiation of 193 and 308nm laser pulses was studied on three kinds of stepped Pt(113) surfaces covered by CO 2 , O 2 and CO 2 , or O 2 and CO at 110K. At 193nm, CO 2 photo-desorption from the first sample was collimated at the surface normal, and its mean translational energy (<E>) was 0.29eV. In the case of a surface covered by O 2 and CO 2 , another CO 2 desorption due to hot-atom collision (<E>=0.17eV) was found to be collimated at 40 o from the surface normal in a plane along the trough. In the case of a surface covered by O 2 and CO, product CO 2 was collimated at +/-24 o in a plane along the trough due to momentum transfer from hot atoms, and <E> was 0.38eV. It is proposed that hot-atom energy decreases with an increase in irradiation wavelength, since the collimation angle and <E> decreased to +/-19 o and 0.28eV under 308nm irradiation.