Conformations and diffusion of n-pentane adsorbed on a metallic surface

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Abstract
The diffusion of n‐pentane molecules on metallic surfaces is modeled by molecular dynamics simulations. On atomically smooth, face‐centered‐cubic (111) crystal surfaces, adsorbed n‐pentanes have several conformational adsorption states, each of which diffuses at a different rate. Diffusion barriers are distinct from intramolecular conformational isomerization barriers. Weak friction is observed. Hopping diffusion is observed near the diffusion threshold. As temperature is raised, correlated barrier crossing and recrossing increases. Adsorbed n‐pentanes slide, transverse to their axes, without changing their orientation with respect to the surface. Conformational changes occur on a longer time scale than diffusional barrier crossing and are restricted by the surface. At temperatures far above the diffusion threshold, partial molecular desorption occurs and conformational isomerization is less restricted. The molecules slide, roll, and tumble continuously across the surface.