THE INFLUENCE OF ELECTRONIC-STRUCTURE ON D-2 ACTIVATED DISSOCIATIVE CHEMISORPTION AT CU85PD15(110)

The activity of a Cu85Pd15{110} surface towards dissociative chemisorp tion of D-2 has been investigated over a range of incident gas conditi ons using a molecular beam. Two different surfaces can be prepared, a disordered (1 x 1) surface with both Cu and Pd in the top layer and an ordered, reconstructed (2 x 1) surface with a top layer of pure Cu an d a first layer with 1/2 monolayer of Pd in an ordered (2 x 1) array [ D.J. Holmes et al., Surf Sci. 227 (1990) 179; M.A. Newton et al., Surf . Sci. 259 (1991) 45]. The alloy shows a Pd derived feature in the den sity of states that shifts upwards towards the Fermi level with increa sing Pd content [R.S. Rao et al., Phys. Rev. B 29 (1984) 1713]. Adsorp tion of D-2 on the Cu85P15{110}(2 x 1) surface is highly activated, ri sing from S-0 approximate to 1.5 x 10(-7) at an energy of 0.13 eV to s imilar to 0.01 at 0.4 eV. This behaviour is similar to that of Cu{111} but S-0 is rather lower than that reported for Cu{110}). The changes to the filled d bands due in the Pd alloy have a minimal effect on the dissociative chemisorption probability, consistent with the absence o f any d band density of states at the Fermi level. The disordered Cu85 Pd15{110}(1 x 1) surface also shows activated dissociative chemisorpti on but with a much larger adsorption probability, S-0 similar to 1 x 1 0(-3). Annealing the surface has a dramatic effect on the sticking pro bability and is attributed to the dissolution of Pd clusters. This beh aviour is contrasted with that of the pure materials in the light of t he well characterised electronic structure of Cu85Pd15{110}.