Structure and bonding of chemisorbed ethylene and ethylidyne on Pt(111) from near edge x-ray absorption fine structure spectroscopy and multiple scattering calculations.

The near edge x-ray absorption fine structure (NEXAFS) spectra of ethylene on Pt(111) at 90 and 300 K have been measured and compared to the spectra calculated using the multiple scattering Xα method for cluster models of adsorbed ethylene and ethylidyne. The results indicate that ethylene is adsorbed in the di-σ configuration (sp3 hybridization) at 90 K, and that the π* orbital retains its identity in this configuration, with no component along the C–C axis. The spectrum obtained at 300 K is attributed to ethylidyne (CCH3) and the calculated spectrum for a cluster consisting of this species bonded symmetrically to three Pt atoms is in good agreement with experiment. The calculations show that the multiple scattering molecular cluster approach is a useful technique for interpreting the NEXAFS spectra of adsorbed molecules. [ABSTRACT FROM AUTHOR]