SITE-SPECIFIC COADSORPTION AT PT(335) AS PROBED BY INFRARED-SPECTROSCOPY - STRUCTURAL ALTERATIONS IN THE CO ADLAYER UNDER AQUEOUS ELECTROCHEMICAL CONDITIONS

Experiments probe the effect of hydrogen co-adsorption on the infrared spectral features of carbon monoxide adsorbed at Pt(335) {Pt(S)-[4(11 1)X(100)]} under aqueous electrochemical conditions. Using intermediat e CO coverages, where it is possible to discern infrared spectral feat ures for CO bound terminally (atop) at edge sites and at terrace sites , the present experiments observe greater alterations in the atop CO p opulation at the step edge compared to the atop CO population on the t errace plane when hydrogen is co-adsorbed under aqueous electrochemica l conditions. These findings suggest that hydrogen is preferentially a dsorbed at step sites on the Pt(335) surface plane and they coincide w ith what has been revealed by recent UHV experiments which probed the effect of co-adsorbing oxygen at Pt(335) in the presence of a partial CO monolayer.