CO interaction with co-adsorbed C2H4 on Cu(111) as revealed by friction with the conduction electrons

Simultaneous measurements of the DC resistance and IR reflectivity changes of thin epitaxially grown copper (111) films have been performed during co- adsorption of CO with C2H4. The linear dependence of these two quantities, which has previously been observed for CO on Cu(lll) films, also holds for this coadsorbed system. Importantly, we have shown that the linearity facto r is independent of the adsorbate type, as predicted by the scattering mode l of the conduction electrons. Co-adsorption of CO with C2H4 results in mar kedly more pronounced changes in IR reflectance and in resistance; these ch anges are higher than the sum of the individual changes of each species. Th e results are interpreted as a consequence of covalent through-metal bondin g of the adsorbates via the lowest unoccupied molecular orbitals, (C) 2000 Elsevier Science B.V. All rights reserved.