DESORPTION AND MOLECULAR-INTERACTIONS ON SURFACES - CO RH(110), CO/RH(100) AND CO/RH(111)/

We present studies of the isothermal desorption of carbon monoxide fro m the three low index rhodium surfaces using time-resolved electron en ergy loss spectroscopy (TREELS). We use a quasiequilibrium model and a pply lattice gas theory and the transfer matrix technique to model the desorption isotherms. With the further assumption that the nearest ne ighbor interaction energy between chemisorbed CO molecules is large an d repulsive, we extract the second and third neighbor lattice energies for all three surfaces. We compare our results with the ordered CO ov erlayer structures reported by low electron energy diffraction measure ments. We find that the lateral interaction energies on all three surf aces exhibit weak but non-negligible repulsion and attraction. We also examine and discuss the validity of the quasiequilibrium assumption i n analyzing desorption measurements. Finally, we compare and discuss t he trends in observed CO structures on various transition metal surfac es. (C) 1997 Elsevier Science B.V.