Orientation dependent CO , production by exposing a CO precovered Pt ( 100 ) surface to gas phase oriented NO

Using a hexapole technique, a beam of gas phase oriented and state selected NO molecules is directed onto a CO precovered Pt(100) surface. Two quadrupole mass analyzers behind the platinum target record the yield of NO and CO, molecules leaving the surface. The platinum single crystal acts like a catalyst and the CO, reaction signal strongly depends on the initial NO orientation, that is to say preferential Nor O-end collisions perpendicular to the surface. At first the orientation asymmetry of the CO, signal, defined positive for a higher N-end collision signal, has a positive initial value of 0.30, 0.16 and 0.07 for substrate temperatures of T, = 120 T, = 130 and T, = 14o”C, respectively. The dependence of the reaction and of the sticking on the initial NO orientation leads to a transition from Eley-Rideal/Harris-Kasemo to Langmuir-Hinshelwood reaction.