INFLUENCE OF POTENTIAL ON METAL-ADSORBATE STRUCTURE - SOLVENT-INDEPENDENT NATURE OF INFRARED-SPECTRA FOR PT(111)/CO

In situ infrared spectra are reported in the C-O stretching (nu-CO) region for saturated CO adlayers on Pt(111) in four nonaqueous solvents; acetonitrile, dimethylformamide, dichloromethane, and tetrahydrofuran, each containing tetraalkylammonium cations, over wide electrode potential ranges, ca. -2.0 to 1.5 V vs SCE. Notably, the spectral features (nu-CO frequencies, CO site occupancies, etc.) are sensitive only to the applied potential, being virtually independent of the solvating medium. Comparisons with spectra obtained in the presence of different cations, and in corresponding aqueous electrochemical and ultrahigh-vacuum environments, demonstrate that the adlayer properties are controlled in each case by the surface potential drop across the adsorbate layer.