Surface Science 251/252 (1991) 965-970 North-Holland 965 Inverse photoemission study of carbon monoxide bonding to transition metals G. Rangelov, N. Memmel, E. Bertel and V. Dose Max-Planck-Institut zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ftir Plasmaphysik, EURA TOM-Association, W-8046 Garching, Germany Received 1 October 1990; accepted for publication 30 October 1990 The unoccupied CO derived bands for the densely packed CO monolayer on Ni(llO), Pd(llO), and Pt(ll0) have been investigated by inverse photoemission. In all three cases four CO derived bands can be observed in the region of the 2n * and 50 * orbitals. For Ni and Pd the band dispersions show the signature of r bands. No evidence is found for unoccupied e contributions, i.e. for 50 donation. However, in Pt the band dispersions are significantly different and hint at a significant 50 donation. The energy position of the CO derived manifold is rather similar for all three metals. These results on the electronic structure are consistent with thermodynamical and vibrational data reported in the literature for the three systems. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP 1. Introduction The bonding of CO on transition metal surfaces is usually discussed in terms of the Blyholder picture, which is outlined on the right-hand side of fig. 1. The deep CO valence orbitals 4a and l?r do not significantly participate in the bonding. The 5a orbital hybridizes with the metal conduction band and splits into a bonding 5a and an anti- bonding 5 u * part. The 5u* orbital is partially co/ Pt (110) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA COlNi (110) CO-M CO,M (eV) 5 i *.* 2n* ,<--__ ,’ ‘7 2rr EF ;zL4U__ . . . d I<-- d WI a \ ,*’ 2n ‘\ = \ ,!- 56 I’ ‘.. In I’ ;----- ,n I’ 56 -5 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA -10 ! Fig. 1. Schematic representation of the CO-metal bond in the Blyholder picture (right side), of the valence bands for CO/Ni and of the valence bands for CO/Pt. The solid lines indicate mainly CO derives bands, the hatched areas mark the range of the metal sp bands and the cross-hatched areas the metal d bands. 0039-6028/91/$03.50 (0 1991 - Elsevier Science Publishers B.V. (North-Holland)