COMPETING ROUTES FOR CHARGE-TRANSFER IN COADSORPTION OF K AND O2 ON GRAPHITE

We have investigated a model co-adsorption system using electron energ y loss spectroscopy. When the dispersed phase of K/graphite is exposed to O2 at 25 K, the charge donated by the alkali is depleted, as evide nced by a reduction of the surface plasmon energy from approximately 3 20 to approximately 130 meV. The co-adsorbed O2 species is molecular, with a vibrational frequency consistent with the 2PI(g) ground state o f O2-. The results demonstrate local transfer of charge from alkali to co-adsorbate, consistent with a simple electrostatic model. By contra st, CO perturbs the K-graphite interaction only weakly.