Field-Dependent Chemisorption of Carbon Monoxide

Ever since the first in situ Infrared spectral measurements of CO adsorbed on metal electrodes, the experimentally observed potential dependence of the vibrations of CO in its chemisorbed state has attracted much attention. This concerns both the intramolecular C-0 stretch and the metal-adsorbate M-CO vibration. Because of the great significance of this system to electrochemical surface science, a separate section devoted to the field-dependent chemisorption of CO on (transition-) metal electrodes is warranted. This is also the electrochemical system that has served as a paradigm for the application of quantum-chemical techniques to field-dependent electrochemistry, starting with the semi-empirical work of Anderson and the ab initio Hariree-Fock based calculations of Bagus and coworkers.  

Further evidence for pronounced field effects on the bonding mechanism of chemisorbed CO came from the work of Illas, Ricart, and co-workers, who combined DFT calculations and SCF-HF calculations including electron correlation effects using the MP2 formalism. These authors were also the first to study field effects of CO chemisorbed on a small 4-atom Pt(lll) cluster, which is the electrode surface for which most of the available experimental results have been obtained. Using a projection operator technique, they showed that both the 5o and 2ti populations of the chemisorbed CO 

In collaboration with the Purdue group, we have carried out detailed analyses of the field-dependent chemisorption of CO on transition-metal (111) surfaces by DFT-GGA calculations on 13-atom clusters.One of the objectives of our studies was to provide relationships between binding energetics, geometries, and vibrational properties, both of the intramolecular C-0 and the metal-adsorbate bond. 

Largely similar results were obtained for the other transition-metal surfaces, i. e. Pd, Ir, and Rh, although only on Rh a site switch is predicted to occur, similarly to Pt. On Ir and Pd, however, the energetic 

The dvoprldF values are seen to be in rough accordance with the dVaxp IdF estimates, although the variations of the former are smaller. These discrepancies are probably due to the role of co-adsorbed solvent in affecting the local electrostatic field. Nevertheless, the larger Stark tuning slopes computed for NO vs. CO are in accordance with experimental observations. 

Decomposition of Field-Induced Frequency Shift (In cm ) for CO Adsorbed in the Atop and Hollow Site on Pt(l 

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Wasileski SA, Koper MTM, Weaver MJ (2001) Field-dependent chemisorption of carbon monoxide on platinum-group (111) surfaces relationships between binding energetics, geometries, and vibrational properties as assessed by density functional theory. J Phys Chem B 105 3518-3530... 

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