Reflection Infrared Study of the Xe-CO Interaction on Pt(335): A New Method for Site Assignment of Chemisorbed Species

Abstract

The interaction of CO and Xe on Pt(335)[Pt4(111)x(100)] has been studied by temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS). TPD results show desorption peaks at approximately 400 K and approximately 500 K from the pure CO layer. The high-temperature peak is related to CO adsorbed on step sites, while the low-temperature peak is related mainly to CO adsorbed on terrace sites. IRAS studies, performed on CO layers after annealing to 290 K, show four subsequently appearing vibrational modes: approximately 2075 and approximately 1880 cm[sup [minus]1] for low [theta][sub CO], and approximately 2092 and approximately 1900 cm[sup [minus]1] for high [theta][sub CO]. Experiments involving Xe coadsorption and isotopic CO site exchange have been conducted, and the four vibrational modes are assigned to terminal and bridged CO adsorbed on step sites for low [theta][sub CO] and on terrace sites for high [theta][sub CO], respectively. The stepwise sequence for CO adsorption on Pt(335) is thus: terminal-bound CO followed by bridge-bound CO on step sites at low [theta][sub CO]-CO, then terminal-bound CO followed by bridge-bound CO on terrace sites at high [theta][sub CO]. 24 refs., 5 figs.