The adsorption of carbon monoxide on rhenium: Basal (0001) and stepped 14 (0001) × (101?1) planes

The influence of surface defects on the adsorption of CO by rhenium is investigated using LEED, AES and linear temperature programmed desorption. On both surfaces, thermal desorption reveals two adsorption states, the lower temperature α state being resolved into two substates, and one β state, all desorbing with first order kinetics. The α state is unaffected by the surface texture, its maximum population being the same on both surfaces, around 4 × 10¹⁴ molecules cm^?2, similar to the value found for poly crystalline rhenium. On the other hand, the β state is strongly dependent on surface structure. On Re(0001) a maximum of 4 × 10¹³ molecules cm^?2 was found, and 2 × 10¹⁴ molecules cm^?2 on the stepped surface. The adsorption is activated and can be increased, by heating to 550 K, to 2 × 10¹⁴ molecules cm^?2 on the basal plane and 3.5 × 10¹⁴ molecules cm^?2 on the stepped surface. Ordered structures are now seen in LEED. Comparison of these results with previous results from polycrystalline rhenium indicate that the dissociation of β-CO on the latter surface must occur at defects other than steps.