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Abstract:
Molecular adsorption is observed on a Ni(110) surface at 80 K. The relative binding energies of the valence ion states as determined by ARUPS are consistent with those in the gas as well as in the condensed phase, and indicate that the electronic structure of the adsorbed molecule is only slightly distorted upon adsorption at this temperature. The adsorbate spectra show E versus k∥ dispersions indicating some long-range order in the adsorbate. The variations in relative ionisation probabilities of the ion states as a function of electron emission angle suggest that the molecular axis is oriented parallel to the surface within ± 20°. Upon heating the adsorbate to above 100 K. (i.e. 140 K) the spectrum changes. A new species causing an increase in work function by 1 eV can be identified. Comparison with calculations suggests that it is an anionic bent CO2 molecule. Electron energy loss studies on this intermediate species support the proposed bent CO2 geometry and favour a coordination site with C2v symmetry. The bent CO2 moiety is stable up to 230 K. Further heating to room temperature leads to dissociation of the bent CO2 molecule into adsorbed CO and O. The CO molecule is oriented with its axis perpendicular to the surface. The bent CO2 species appears to be a precursor to dissociation. Results on CO2 adsorption on an oxygen precovered surface show that CO2 interacts with oxygen at 85 K. Upon heating the co-adsorbate to near room temperature a reaction product is formed the nature of which cannot yet be clearly identified.
