Molecular beam study of dissociative sticking of methane on Ni(100)

Abstract

This paper reports a detailed molecular beam study of the dissociative sticking of methane incident on clean Ni(100). It is demonstrated that the sticking coefficient depends strongly on the translational energy of the molecule. It is also observed that an increase in the vibrational energy of the methane leads to a dramatic enhancement of the sticking, emphasizing that the initial vibrational state is of crucial importance. These results are consistent with a mechanism of direct activated dissociative chemisorption where the dynamics is dominated by a barrier in the potential energy surface mainly located in the vibrational coordinates. Normal-energy scaling is only approximately observed. The effect of surface temperature is also investigated but is found to be smaller than activation by translational or vibrational energy. A simplified analysis in terms of state resolved sticking curves, Sν(Ei), considering only the vibrational C–H stretch modes of methane as relevant for the sticking, gives a good description of the data. These sticking curves enables a calculation of the thermal sticking coefficient which is found to be in excellent agreement with bulb experiments directly probing this.