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

Abstract

The interaction dynamics of NO with the reactive Ru(0001) surface has been investigated with the use of supersonic molecular beam techniques. Helium scattering, King and Wells sticking measurements and time-of-flight (TOF) experiments are performed. The initial sticking coefficient is remarkably high with incident energy, varying from unity at thermal energies to ∽90% for 0.25⩽E_i⩽2.4 eV and does not seem to depend on surface temperature for 400⩽T_s⩽850 K. Counter intuitively, the non-sticking ∽10% of the incident flux has only about 12% translational energy transfer in the specular scattering direction. Molecular sticking is observed at low surface temperatures for above thermal incident energies, up to at least 0.45 eV.

An attempt is made to distinguish between molecular precursor mediated pathways and direct dissociation. In order to account for the surprisingly constant initial sticking coefficients, the opening of a direct dissociative channel is proposed for beam energies exceeding the depth of the molecular chemisorption well. Several open problems are identified.