Surface diffusion of n-alkanes on Ru(001)

Abstract

The surface diffusion of n‐alkanes on Ru(001) was measured using laser‐induced thermal desorption (LITD) techniques. The surface diffusion coefficients for propane, n‐butane, n‐pentane, and n‐hexane all displayed Arrhenius behavior. The surface diffusion activation energies increased linearly with carbon chain length from E_dif =3.0±0.1 kcal/mol for propane to E_dif =4.8±0.2 kcal/mol for n‐hexane. In contrast, the surface diffusion preexponentials remained nearly constant at D₀ ≂0.15 cm² /s. Measurements performed at different coverages also revealed that the surface diffusion coefficients were coverage‐independent for all the n‐alkanes on Ru(001). The surface corrugation ratio Ω was defined as the ratio of the diffusion activation energy to the desorption activation energy, Ω=E_dif /E_des . The surface corrugation ratio was observed to be remarkably constant at Ω≂0.3 for all the n‐alkanes. This constant corrugation ratio indicated a linear scaling between the diffusion activation energy and the desorption activation energy. This behavior also suggested that the n‐alkanes move with a rigid configuration parallel to the Ru(001) surface.