In this work, we present results of a periodic density-functional theory study of the adsorption of carbon monoxide (CO) and hydroxyl (OH) on platinum, ruthenium, and a series on platinum-ruthenium alloys. The surfaces are modeled as four-layer slabs. The binding energies and geometries of CO and OH are computed, as well as the vibrational properties of chemisorbed CO. We find that the mixing of Pt by Ru leads to a weaker bond of both CO and OH to the Pt sites, whereas mixing of Ru by Pt causes a stronger bond of CO and OH to the Ru sites. The binding energy trends for CO do not show a clear-cut relationship with its vibrational characteristics. The binding energy changes are electronic alloying effects that can be explained by the d band shift model of Hammer and Nørskov. From our calculations, we can conclude that for a good CO oxidation fuel cell catalyst, it is important to have both Pt sites (which bind CO weakly) and Ru sites (which bind OH strongly) on the surface. However, if a low surface coverage of CO is required, which may be case for the oxidation of H 2 in the presence of a small amount of CO, Ru with a monolayer of Pt might be more advantageous, as this is the Pt-Ru surface that shows the weakest CO binding.

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Femtosecond mid-infrared pump–probe spectroscopy is used to study the orientational relaxation of HDO molecules dissolved in liquid D2O. In this technique, the excitation of the O–H stretch vibration is used as a label in order to follow the orientational motion of the HDO molecules. The decay of the anisotropy is nonexponential with a typical time scale of 1 ps and can be described with a model in which the reorientation time depends on frequency and in which the previously observed spectral diffusion is incorporated. From the frequency and temperature dependence of the anisotropy decay, the activation energy for reorientation can be derived. This activation energy is found to increase with increasing hydrogen bond strength.

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