Surface diffusion of CO molecules on Pd{111} studied with photoelectron emission microscopy

The diffusion of CO on Pd{111} has been studied with photoelectron emission microscopy by monitoring the time evolution of CO concentration along flat, quasi-one-dimensional terraces of the surface. From the analysis of the concentration profiles the activation energy and the pre-factor for the diffusion coefficient are determined to be E_a = 175(±12) meV and D_o = 2.2 × 10 ^-3 cm ² s ^-1 respectively. Previous, "macroscopic" measurements of CO diffusion on metals have probably resulted in too high values for E_a due to the neglect of the effects of the surface microtopography.