Dynamics of molecular chemisorption of N2 on the Ru(001) surface

The chemisorption of N2 on Ru(001) has been studied using supersonic molecular beam techniques. The initial molecular chemisorption probability, S0, was measured as a function of incident energy, Ei, from 0.021 to 0.90 eV and angle of incidence, θ, from 0° to 60° at a surface temperature of 77 K. At a normal angle of incidence, the value of S0 decreases with increasing kinetic energy in the low and intermediate energy regimes and is constant in a higher energy (0.4 eV<Ei<0.7 eV) regime. As the angle of incidence increases, the value of S0 decreases more rapidly with Ei at low energies. At θ=60°, S0 decreases with increasing kinetic energy, passes through a local minimum near Ei=0.2 eV, and then increases to the same constant value as in the normal incidence case. At Ei=0.90 eV, the most energetic beam used in this study, the value of S0 decreases slightly from this constant value. Similar measured trends in the angular and energy dependence, particularly at intermediate energies, have not been reported previously for a molecular chemisorption system, and we qualitatively describe this behavior by combining a trapping-mediated mechanism (dominant at low incident energies) and a direct molecular chemisorption mechanism (dominant at high incident energies). We also report measurements of the initial dissociative chemisorption probability of N2 on Ru(001) and conclude that this probability at Ei=1.25 eV and normal incidence does not exceed 1×10−3 at a surface temperature of 600 K.