STICKING AND SCATTERING OF GAS-PHASE ORIENTED NO AT PT(100) AS A FUNCTION OF THE TRANSLATIONAL ENERGY AND OF MOLECULAR-ORIENTATION

Using a hexapole technique, a pulsed beam of state-selected NO molecules is focused onto a Pt(100) surface with orientation of the molecular axis so that either preferential N-end or O-end collisions occur with the surface. From the analysis of the partial NO pressure behind the crystal the initial sticking probabilities for oriented as well as for unoriented NO molecules can be determined. The translational energy of the molecules is varied between 100 and 350 meV by seeding in helium at different NO concentrations. The sticking probability is larger for N-end collisions and decreases with increasing translational energy. Likewise, a similar decrease is also observed in the orientation-dependent scattering asymmetry. The results show that both direct chemisorption and trapping into a precursor state occur preferentially for N-end collisions.