HIGH-RESOLUTION ELECTRON-ENERGY LOSS SPECTROSCOPIC STUDY OF CO2 ADSORBED ON RE(0001)

The adsorption geometry and dissociation of CO//2 on Re(0001) were studied by high-resolution electron energy loss spectroscopy (HREELS) over the crystal temperature range of 85-150 K. It was found that CO//2 adsorbs as an undistorted linear molecule with its axis parallel to the surface up to a crystal temperature of 120 plus or minus 5 K. It is characterized by vibrational losses that are very similar to the frequencies of the gas-phase molecule. In the temperature range of 120-135 K a fraction of the adsorbed molecules desorb and the rest transform to an intermediate tentatively identified as a bent CO//2** minus which dissociates to CO//a plus O//a at 135 K and above. Similar results are obtained on an oxidized rhenium surface. The effect of post dosing of oxygen on the vibrational losses of CO adsorbed at 300 K was studied as a model for the CO//2 fragments on the surface and was found to be negligible.