Molecular beam study on interaction dynamics in a reactive system: NO on bare Ru(0001)

The interaction dynamics of NO with the reactive Ru(0001) surface has been investigated with the use of supersonic molecular beam techniques. Helium s cattering, King and Wells sticking measurements and time-of-flight (TOF) ex periments are performed. The initial sticking coefficient is remarkably hig h with incident energy, varying from unity at thermal energies to similar t o 90% for 0.25 less than or equal to E (i) less than or equal to 2.4 eV and does not seem to depend on surface temperature for 400 less than or equal to T-s less than or equal to 850 K. Counter intuitively, the non-sticking s imilar to 10% of the incident flux has only about 12% translational energy transfer in the specular scattering direction. Molecular sticking is observ ed at low surface temperatures for above thermal incident energies, up to a t least 0.45 eV. An attempt is made to distinguish between molecular precursor mediated path ways and direct dissociation. In order to account for the surprisingly cons tant initial sticking coefficients, the opening of a direct dissociative ch annel is proposed for beam energies exceeding the depth of the molecular ch emisorption well. Several open problems are identified.