Na-induced bonding and bond-length changes for CO on Pt(111): A near-edge x-ray-absorption fine-structure study

Near-edge x-ray absorption fine-structure studies above the C and O K edges for CO on Pt(111) reveal a 4-eV shift of the σ shape resonance when Na(0.2 monolayer) is coabsorbed. This allows determination of a Na-induced (0.12±0.03)-Å expansion of the C-O bond. Na does not affect the vertical molecular orientation on the surface. Reduction and broadening of the 1s→2${\mathrm{\pi }}^{\mathrm{*}}$ resonance and the CO bond lengthening in the presence of Na signifies substantially increased metal to CO backbonding.