Theoretical studies of the interactions of ethylene and formaldehyde with gold clusters

We studied the adsorption of C2H4 and CH2O on the gold clusters Au-n (n=1-5) in various adsorption modes using density functional theory PW91 functional. We found that the binding energies of pi-C2H4 and pi and O-sigma modes of CH2O increase first and then decrease with the cluster size. Natural bonding orbital (NBO) analyses reveal that the donor-acceptor interaction plays an important role in these adsorption complexes and there is a nice linear relationship between the calculated binding energy and the stabilization energy estimated with second-order perturbation theory in the framework of NBO analysis. It is demonstrated that the bonding interaction between adsorbates and clusters follows the di-sigma>pi>O-sigma mode. However, due to adsorption induced structural deformation of adsorbates and clusters, the binding energies of different adsorption modes are comparable. It is shown that C2H4 interacts more strongly with the clusters than CH2O does and that the previously assigned adsorption mode of C2H4 on Au/MgO may not be the pi modes, but the C-sigma configuration.