EFFECTS OF PREADSORBED OXYGEN ON THE BONDING AND DESORPTION-KINETICS OF CO ON NI(110)

The effects of oxygen preadsorption on CO adsorption and CO desorption kinetics have been studied by temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). It is found that preadsorbed oxygen decreased total CO uptake at 120 K by no more than 20% even though the adsorption and desorption energies are strongly affected. The presence of oxygen causes several new desorption states to appear in the TPD whose populations depend sensitively upon oxygen predose. Using published results for the structure of oxygen covered Ni(110) and the present HREELS measurements, the desorption states have been assigned to structurally distinct bonding sites. Using the variation in heating rates method, the first order desorption energies and preexponential factors are obtained as a function of CO coverage for various oxygen predoses. The relationship between the desorption energies and the bonding sites, especially with regard to the distance of CO from neighboring oxygen atoms, is discussed.