Influence of Multielectron Excitations on the Band Structure of Adsorbate Overlayers

Photoelectron spectra from ordered CO on Cu(111) exhibit anomalously small $4\sigma$ band dispersion compared to all other CO adsorption systems previously studied. The bonding $5\sigma$ band displays normal one-electron dispersion. It is shown that the energy dependence of the $4\sigma$ band expected for a single-particle system is transferred into $k$-dependent intensity variations of the quasiparticle excitation and the intense satellite line ∼2 eV lower in energy. The first moment of the spectral weight function over this energy range recovers the anticipated one-electron band dispersion.