ETHYLENE ADSORPTION ON THE CU(111) SURFACE - DFT CLUSTER STUDIES

Experimental results for ethylene adsorbed at metal surfaces indicate major changes in the adsorbate structure, in particular an increased C -C distance, while the adsorption energy is found to be small. These f indings can be explained by competitive adsorbate-substrate binding as evidenced in ab initio DFT cluster studies using a Cu-7(4,3)C2H4 clus ter to simulate C2H4 adsorption on Cu(111). The calculations suggest t hat the adsorbate stabilizes in a cross-bridge orientation on Cu(lll) where its C-C axis lies almost parallel to the surface and the two C c enters point towards adjacent 3-fold fcc and hcp hollow sites. Further , the cluster results confirm the increased C-C distance of the adsorb ate and predict bending of its CH2 ends near the surface where the lat ter has not been observed so far. The distortion of the adsorbate is c ombined with rehybridization resulting in C-C bond weakening and incre ased adsorbate-substrate coupling characterized by a Dewar-Chatt-Dunca nson type donation scheme.