Vibrational Line Broadening Mechanisms for Molecules Adsorbed on Metal Surfaces

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This project is in the general area of analytical and surface chemistry and in the subfield of surface vibrational spectroscopy. High resolution vibrational spectra of a variety of molecular species adsorbed on metal surfaces will be measured using Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS). The limits of IRAS will be extended: 1) to study adsorbate-substrate vibrations; 2) to characterize the temperature dependence of vibrational line shapes at temperatures as low as 10 K; 3) to characterize the line shapes of overtones; 4) to characterize and analyze the influence of order-disorder phase transitions on adsorbate lineshapes. Chemical systems to be studied include the molecular species phosphorus trifluoride, carbon monoxide and ethylidyne on single-crystal faces of platinum and nickel. The intrinsic lineshapes of vibrational spectra contain information on adsorbate-adsorbate interactions, the extent of vibrational coupling to other modes, and the lower bound of other vibrational modes. The wide range of temperatures that will be employed in this study and the possibility of freezing out phonon mechamisms will permit discrimination among various competing mechanisms of line broadening.