QUANTUM-CHEMISTRY AND INSITU FTIR SPECTROSCOPY STUDIES ON POTENTIAL-DEPENDENT PROPERTIES OF CO ADSORBED ON PT ELECTRODES

The electronic and vibrational properties of CO adsorbed on Pt electro des at different potentials have been studied, by using methods of sel f-consistent-charge discrete variational Xalpha (SCC-DV-Xalpha) cluste r calculations and in situ FTir spectroscopy. Two new models have been developed and verified to be successful: (1) using a ''metallic state cluster'' to imitate a metal (electrode) surface; and (2) charging th e cluster and shifting its Fermi level (epsilon(f)) to simulate, accor ding to the relation of -depsilon(f) = e dE, quantitatively the variat ion of the electrode potential (E). It is shown that the binding of Pt -CO is dominated by the electric charge transfer of dpi(Pt) double-lin e arrow pointing right 2pi(CO), while that of sigma(CO) double-line a rrow pointing right Pt is less important in this binding. The electron occupancy of the 2pi orbital of CO(ads) weakens the C=O bond and dec reases the nu(CO). Variation of E mainly influences the charge transfe r process of dpi(Pt) double-line arrow pointing right 2pi(CO), but ha rdly influences that of sigma(CO) double-line arrow pointing right Pt. A linear potential-dependence of nu(CO) has been shown and the calcul ated dnu(CO)/dE = 35.0 cm-1 V-1. All results of calculations coincide with the ir experimental data.