INTERACTIONS BETWEEN CHEMISORBED CO AND OXYGEN ON NI(111)

Infrared reflection absorption spectroscopy (IRAS), low energy electron diffraction (LEED), work function (DELTAPHI), and temperature programmed desorption (TPD) have been used to characterize the interactions between chemisorbed CO and oxygen on Ni(111). It has been found that chemisorbed oxygen exhibits both a long range and a short range effect on chemisorbed CO on Ni(111). The short range interaction between chemisorbed oxygen and chemisorbed CO produces a perturbed terminal-CO species, designated as CO*, with a singleton frequency 41 cm-1 higher than that of the unperturbed terminal-CO. The CO* species is found to adsorb on Ni sites which are the nearest neighbors to the oxygen adatoms adsorbed in the threefold sites. The long range interaction between the two coadsorbates also produces a blue-shift in the singleton frequency of the bridged-CO, and a reduction in the CO saturation coverage. A comparison of the interactional effect of oxygen and sulfur on chemisorbed CO indicates that the size of an electronegative species and its projection above the surface is more important than the electronegativity in determining the strength of the poisoning effect of the electronegative species on chemisorbed CO.