Comparisons between coverage-dependent infrared frequencies for carbon monoxide adsorbed on ordered Pt(111), Pt(100), and Pt(110) in electrochemical and ultrahigh-vacuum environments

Infrared spectra measured for carbon monoxide adsorbed on Pt(111), (100) and (110) surfaces in aqueous 0.1M HClO sub 4 as a function of carbon monoxide coverage, theta sub CO , and electrode potential, E, are compared with coverage-dependent infrared spectra for the corresponding interfaces in ultrahigh vacuum (uhv). The electrochemical theta sub CO values at saturation on all three faces are similar to those in uhv. The terminal C--O stretching frequencies, nu exp t sub CO , and band intensities are markedly dependent on the crystallographic orientation at a given electrode potential. Extrapolation of the electrochemical coverage-dependent nu exp t sub CO values to electrode potentials corresponding to the appropriate work function for the anhydrous uhv Pt/CO surfaces yields similar nu exp t sub CO -- theta sub CO plots as are observed for the latter interfaces. This suggests that the well-known effects of the double-layer solvating environment upon nu sub CO are primarily electrostatic in origin. Graphs, spectra. 51 ref.--AA