Nature of the Binding of a c(2×2)-CO Overlayer on Ag(001) and Surface Mediated Intermolecular Coupling

Abstract

We present a first-principles study of the nature of the binding of a c(2×2)-CO overlayer on Ag(001) and of the origin of CO-CO interactions upon adsorption. Electronic structural changes induced by molecular adsorption provide an interpretation for earlier X-ray photoemission valence band spectra of CO/Ag(001). Our results establish that CO chemisorbs on clean Ag(001) and follows the Blyholder model of donation and back-donation between CO and metal orbitals. We analyze the origin of the dispersion of the C-O stretch mode and attest that it is caused by the metal-CO coupling. Specifically, the coupling of CO to Ag, although the weakest of those between it and transition and other noble metals, greatly enhances the intermolecular force constants. We also find that the response of the charge density around CO is much stronger and of longer range when the molecule stretches than when it rigidly vibrates against the surface. This difference explains why the C-O stretch mode disperses while the Ag-CO stretch mode does not.

Combined Scanning Tunneling Microscopy and High-Resolution Electron Energy Loss Spectroscopy Study on the Adsorption State of CO on Ag(001)

“…Ortigoza et al 16 argued that the vibrational energy of the IS mode alone could not be used invariably to evaluate the metal− CO interaction because dynamic couplings among the neighboring CO molecules and from the substrate 23 also significantly affect the vibrational energy of the IS mode. They concluded that the apparent paradoxical relationship between the vibrational energy of the IS mode and the bond strength, which had been observed on Ag(001) and Cu(001), was due to the different contributions of the dynamic couplings to the internal force constant of CO. Qualitatively, the argument that the dynamic couplings affect the bonding of CO on the metal, even though the metal−CO interaction is weak, holds.…”

“…This value of 256 meV indicates that the C–O bond is softened so that the interaction of CO with Ag(001) should be comparable to that of Cu(001). − However, considering that CO certainly adsorbs onto Cu(001) even above 100 K while no CO adsorption on Ag(001) is usually observed at 100 K, it is clear that the interaction of CO with Ag(001) is weaker than that with Cu(001). Recently, Ortigoza et al , tried to solve this puzzle using a theoretical method. They calculated the vibrational energies and binding energy of CO on Ag(001) and demonstrated that the vibrational energy of the IS mode was almost the same as or slightly higher than that on Cu(001).…”

CO Adsorption on Ag Nanoclusters Supported on Carbon Nanotube: A Molecular Dynamics Study

“…Their results indicate that CO is chemisorbed on Ag(001) surface and follows Blyholder model of donation and back-donation of electrons between CO and metal orbitals. 34 Bloch et al investigated adsorption of CO and CO 2 on the large pore sized Ag/SiO 2 nanocomposite using the microcalorimetry method. 35 Their results indicate that the Ag/SiO 2 nanocomposite can be considered as an interesting candidate for the adsorption of trace amounts of CO in the presence of CO 2 .…”

“…They found that the CO molecules are chemisorbed very weakly on the Ag(001) surface. Ortigoza et al presented a first-principles study of the nature of the binding of a c(2 × 2)-CO overlayer on Ag(001) and the origin of CO–CO interactions during the adsorption process . They proposed that the binding of CO aggregately enhances the intermolecular (CO–CO) force constants.…”

The perturbation energy: A missing key to understand the “nobleness” of bulk gold

“…Moreover, ab-initio calculations of the charge density and density of states show that CO does chemisorb on Ag through the donation and backdonation (Blyholder 50 ) mechanism, and this happens in part precisely because f m 1. 51 Ionic binding. In modeling the E ionic contribution, we consider an ideal ionic bond whose strength is determined by three input variables: (1) the metal-O charge exchange, which accounts for a binding-energy reduction because of charge removal from the metal atom (i.e., the work function) and a binding-energy increase because that charge is gained by O (electron affinity); (2) the binding-energy increase by the electrostatic metal-O attraction; and (3) the bindingenergy decrease because of the electrostatic metal-metal repulsion between the three metal atoms that lose electronic charge upon oxygen adsorption (see Eq.…”