SEMIEMPIRICAL CALCULATIONS OF THE VIBRATIONAL FREQUENCY OF CARBON-MONOXIDE ADSORBED ON NOBLE-METAL SINGLE-CRYSTAL SURFACES

In this work we perform a theoretical analysis of the shift of the obs erved IR reflection-absorption spectroscopy (IRRAS) band of CO adsorbe d on Pt(111), Rh(111) and Pt(100) single crystals as a function of bot h the degree of CO surface coverage and the electric potential applied at either the metal-vacuum or the metal-solution interface. The wavef unctions obtained using a modified extended Huckel molecular orbital ( EHMO) method are used to predict the vibrational frequency data. The P t(110), Rh(111) and Pt(111) single crystals are modelled by bilayer cl usters of 25 and 22 atoms respectively. A theoretical description of t he observed IRRAS shift is analysed by means of a population analysis of CO molecular orbitals, which confirms the donation-back-donation mo del.