ADSORPTION OF OXYGEN ON CU(100) .2. MOLECULAR ADSORPTION AND DISSOCIATION BY MEANS OF O-K-EDGE X-RAY-ABSORPTION FINE-STRUCTURE

The structural and dynamical properties of molecular oxygen in submono layer coverage adsorbed on Cu(100) were investigated by means of oxyge n K-edge photoabsorption. The adsorption geometry of the O-2 molecules , as well as the disorder and anharmonic contributions to the pair dis tribution function for the first-nearest-neighbor O-Cu shell were quan titatively determined for well-defined sequential molecular states of physisorption and chemisorption. The O-2 molecules are found to adsorb in a tilted configuration. Furthermore, the O-Cu interatomic pair pot entials are estimated. It is found that the nearest-neighbor O-Cu bond varies only slightly as the strength of chemisorption increases, in o pposition to a strong O-O bond length and other O-Cu pair-potential pa rameter variations.