Desorption of products in 193 nm photo-induced reactions in (O2+CO) adlayers on Pt(112)

The spatial distributions of desorbing products were examined in 193 nm photo-induced reactions in O-2 + CO adlayers on stepped Pt(112) = [ (s) 3( 111) x (001)]. At high coverage of O-2 ( a) and CO( a), both O-2 and CO2 desorption collimated closely along the (111) terrace normal. The results were compared with those in thermal CO oxidation, and the origin of the collimation angle shift in the latter is discussed. On the other hand, at low CO( a) coverage, O-2 and CO2 desorption collimated in inclined ways in the plane along the surface trough. At these collimation positions, the kinetic energy of desorbing O-2 and CO2 was maximal, confirming the hot-atom collision mechanism.