The Chemisorption of CO on Cu: An Ab Initio Cluster Model Study
We have used ab initio Hartree-Fock wave functions for a Cu5CO cluster to model the interaction of CO with a Cu surface at the head-on absorption site. For a fixed CO distance, 2.173 bohr, we have obtained an interaction curve for various Cu to C distances.
With this curve, we are able to derive the Cu-C stretching frequency, the equilibrium bond distance, and the chemisorption bond strength. The stretching frequency is calculated to be 31 meV which is reasonably close to the 43 meV EELS loss observed by Andersson. The bond distance and stength are also in reasonable agreement with observed values. This agreement is strong evidence that the theoretical approach, including both choice of cluster and the use of SCF molecular orbital theory, provides a good representation of the interaction of CO with a real Cu surface. The nature of this interaction will be discussed based on an analysis of the cluster wave functions.