TOWARD UNDERSTANDING PHOTOEMISSION IN K+CO COADSORPTION SYSTEMS

Alkali-induced changes in electronic energy levels, observed in photoemission from CO on transition-metal surfaces, are examined theoretically and shown to be consistent with the formation of two-dimensional ionic islands in the coadsorbed system. A point-charge model is applied to the K + CO system to calculate the levels. The analysis reveals that significant screening of the CO levels, by the extra electron in the K-modified anion, is masked by an equally large electrostatic stabilization of the electrons on the CO site by the Madelung potential (~ 8 eV) of the K+-CO−layer. The model explains the splitting of the 1π-derived level, by ~ 1 eV, without requiring any symmetry lowering of the molecular geometry. The results are in reasonable agreement with experimental observations and compare favorably with more sophisticated calculations. © 1990, American Vacuum Society. All rights reserved.