How carbon monoxide adsorbs in different sites

The interplay between the electronic and the geometric structure of adsorba tes is of fundamental importance for the understanding of many surface phen omena. Using x-ray emission spectroscopy and ab initio cluster calculations , this issue has been investigated in unprecedented detail for CO adsorptio n in different adsorption sites. The investigation establishes pi bonding a nd sigma repulsion, both increasing with the number of coordinated metal at oms. The two contributions partly compensate each other, leading to only sm all differences in adsorption energies for the different adsorption sites d espite very large variations in the electronic structure.