COADSORPTION OF K AND CO ON PD CLUSTERS - A DENSITY-FUNCTIONAL STUDY

The effect of potassium on the electronic and vibrational properties of CO chemisorbed on transition metal surfaces has been investigated using cluster models. The local spin density approximation has been used to determine the electronic properties and vibrational frequency shifts of CO chemisorbed on Pd clusters in the presence of adsorbed potassium atoms. It is shown that the most important contributions to the large vibrational shifts observed experimentally are due to a polarization of the electron distribution of the cluster in response to the field created by the coadsorbed positive ions. This polarization leads primarily to an increase of the population of the 2 pi* antibonding orbital of CO. There are no appreciable direct electronic interactions between K and CO. The electronic interaction through the metal is of short range, of the order of 5 Angstrom.