COLLISION OF ORIENTED NO WITH NI(100) AND WITH ORIENTED CO ON NI(100)

The interaction between gas-phase oriented NO molecules with Ni(100) has been investigated by means of pulsed supersonic molecular beam, hexapole and time-of-flight techniques. With TOF we examined the NO molecules leaving the clean Ni(100) surface. A velocity distribution commensurate with the surface temperature was observed. The time-integrated signal of the scattered NO beam shows an orientation asymmetry of A(Sc) = 0.38 +/- 0.05 with respect to the NO and ON initial orientation. An initial sticking probability of 0.27 and 0.30 for preferential O-end and N-end collisions, respectively, at a c(2 x 2) saturated layer of CO was also obtained. Taking the degree of orientation of the NO molecules into account, this leads to an asymmetry of A(St) = 0.5 +/- 0.1 independent of coverage. The CO molecules displaced by NO were simultaneously recorded. The CO signal shows an asymmetry with respect to the NO orientation, as well. Two different displacement mechanisms are discussed to explain this behavior.