Probing surface short range order and inter-adsorbate interactions through IR vibrational spectroscopy: CO on Cu(100).

It is demonstrated that surface vibrational spectroscopy can be used to probe local ordering of adsorbates and the nature of inter-adsorbate interactions through dynamical dipole coupling among neighboring adsorbates. Our studies show that for CO adsorbed on Cu(100), first and second nearest neighbor interactions are repulsive. This repulsion prevents the formation of long range ordered structures at low and medium coverages and can be best understood as an adsorbate induced modification in the local electron density, i.e., Friedel oscillation.