ADSORPTION OF H-2 AND CO ON MN/FE(110) SURFACES

Mn-covered Fe(110) surfaces were prepared by vapor-deposition at 130 K and annealing at 635 K for 15 s. H-2 and CO were adsorbed on these Mn/Fe(110) surfaces at 130 K and analyzed by thermal desorption spectroscopy (TDS) and O 1s X-ray photoelectron spectroscopy (XPS). Compared to pure Fe(110), Mn caused a drastic decrease in the sticking probability of H-2, indicative of an increase in the barrier for H-2 dissociation. Near Mn monolayer coverage there was a slight increase in the adsorption energy of hydrogen. For CO a lowering of the activation barrier of dissociation due to Mn was observed. Although molecular CO adsorbed on Mn/Fe(110) at a rate equal to that on Fe(110), the dissociation of CO started already at 223 K on Mn-covered Fe compared to > 373 K on clean Fe(110). The amount of dissociated CO at 523 K was 14 and 80% of the initial coverage for Fe(110) and Mn/Fe(110), respectively. Mn/Fe synergism on CO adsorption was most clearly noted at submonolayer Mn coverage. Changes in the peak temperature of the molecular CO state coupled to the increased amount of dissociated CO are suggestive of a significantly altered molecular adsorption well and weakened metal-CO bonding.