The properties of CO and K coadsorbed on Pd(100) surface

Low energy electron diffraction (LEED) measurements showed a few weak and two sharp patterns (2×2)R45° and (×)R45° at θK=0.25 and θK=0.50 (monolayer), respectively, for the K+CO coadsorbed layer. Preadsorbed potassium markedly increased the activation energy for CO desorption from 128 kJ/mol at θK=0 to 163 kJ/mol at θK=0.44 (monolayer). The sticking probability remained constant in the range θK=0.0–0.30, but radically decreased above this potassium coverage. The work function of the potassium dosed surface (θK=0.1–0.25) increased sharply following CO adsorption suggesting a high negative charge on CO molecule. A strong electronic interaction between CO and the K/Pd system was also revealed by electron energy loss spectroscopic (EELS) studies. This consisted of a significant decrease in the intensity of the CO loss observed on a clean Pd surface at 12.5–13.0 eV and the simultaneous development of a new loss feature at 24.5–25 eV.