A structural study of a C3H3 species coadsorbed with CO on Pd(1Â 1Â 1)

The combination of chemical-state-specific C 1s scanned-energy mode photoelectron diffraction (PhD) and O K-edge near-edge X-ray absorption fine structure (NEXAFS) has been used to determine the local adsorption geometry of the coadsorbed C3H3 and CO species formed on Pd(1 1 1) by dissociation of molecular furan. CO is found to adopt the same geometry as in the Pd(1 1 1)c(4 × 2)-CO phase, occupying the two inequivalent three-fold coordinated hollow sites with the C-O axis perpendicular to the surface. C3H3 is found to lie with its molecular plane almost parallel to the surface, most probably with the two 'outer' C atoms in equivalent off-atop sites, although the PhD analysis formally fails to distinguish between two distinct local adsorption sites.