Lifetime of excited electronic states at surfaces: CO-(2 pi*) resonance onCu(111) and Cu(100) surfaces

A model study of the (2 pi*) resonance in the CO/Cu(111) and CO/Cu(100) sys tems is presented. Although the CO-(2 pi*) resonance is located inside the surface projected band gap in both systems, it is found to be very short-li ved. These results are at variance with the apparently similar alkali/Cu sy stems where a strong reduction of the resonance decay by one-electron trans fer to the substrate as compared to a free-electron metal surface is observ ed and attributed to the presence of the surface projected band gap. The di fferences between the two systems are analysed, allowing a discussion of th e situations where a projected band gap induced stabilisation can be expect ed. The present results are compared with recent experimental results obtai ned by time resolved 2-photon photo emission. (C) 2001 Published by Elsevie r Science B.V.