X-ray emission spectroscopy and density functional study of CO/Fe(100)

We report x-ray emission and absorption spectroscopy studies of the electronic structure of the pre-dissociative alpha(3) phase of CO bound at hollow sites of Fe(100) as well as of the on-top bound species in the high-coverage alpha(1) phase. The analysis is supported by density functional calculations of structures and spectra. The bonding of "lying down" CO in the hollow site is well described in terms of pi to pi* charge transfer made possible through bonding interaction also at the oxygen in the minority spin-channel. The on-top CO in the mixed, high-coverage alpha(1) phase is found to be tilted due to adsorbate-adsorbate interaction, but still with bonding mainly characteristic of "vertical" on-top adsorbed CO similar to other transition-metal surfaces. (C) 2012 American Institute of Physics. [doi:10.1063/1.3675834]