Table shows the diffusion coefficients calculated using equation 3 at three different temperatures for the 8 adsorbates considered here. An example of the MSD fitting procedure is shown in Fig. . Consistent with increased adsorbate mobility at higher temperatures, we obtain larger diffusion coefficients at 400 K compared to 300 and 350 K. Comparing across different adsorbates, we observe that methyl shows the highest diffusivity (2.38 x10 -7 m 2 /s at 400 K) that is about two orders of magnitude higher than strongly bound adsorbates such as C, O and CH. The diffusivity of other species (i.e. H, OH, CH 2 , and ethyl) lies in between these two extremes. Using equation 4, the temperature-dependent diffusion coefficients are used to obtain apparent activation energies for the overall diffusion process. Consistent with the adsorbate surface density histograms discussed previously, we observe near-perfect Arrhenius behaviour for the atomic adsorbates (Fig. .) As shown in Fig. , slightly larger deviations are observed for molecular adsorbates.