Lifetime of excited electronic states at surfaces: CO−(2π*) resonance on Cu(1 1 1) and Cu(1 0 0) surfaces

A model study of the (2π*) resonance in the CO/Cu(1 1 1) and CO/Cu(1 0 0) systems is presented. Although the CO−(2π*) resonance is located inside the surface projected band gap in both systems, it is found to be very short-lived. These results are at variance with the apparently similar alkali/Cu systems where a strong reduction of the resonance decay by one-electron transfer to the substrate as compared to a free-electron metal surface is observed and attributed to the presence of the surface projected band gap. The differences between the two systems are analysed, allowing a discussion of the situations where a projected band gap induced stabilisation can be expected. The present results are compared with recent experimental results obtained by time resolved 2-photon photo emission.