Adsorption of oxygen on Cu(100). II. Molecular adsorption and dissociation by means of OK-edge x-ray-absorption fine structure

The structural and dynamical properties of molecular oxygen in submonolayer coverage adsorbed on Cu(100) were investigated by means of oxygen K-edge photoabsorption. The adsorption geometry of the ${\mathrm{O}}_2$ molecules, as well as the disorder and anharmonic contributions to the pair distribution function for the first-nearest-neighbor O-Cu shell were quantitatively determined for well-defined sequential molecular states of physisorption and chemisorption. The ${\mathrm{O}}_2$ molecules are found to adsorb in a tilted configuration. Furthermore, the O-Cu interatomic pair potentials are estimated. It is found that the nearest-neighbor O-Cu bond varies only slightly as the strength of chemisorption increases, in opposition to a strong O-O bond length and other O-Cu pair-potential parameter variations.