Position of the σ-shape and π resonances of C₂H₂, C₂H₄ and C₂H₆ on Cu(100) at 60 K: A NEXAFS study

The position of the π and σ resonances in the C K edge spectra are determined for multilayer and submonolayer coverages of C2H2, C2H4 and C2H6 at 60 K, on a Cu(100) surface. The majority of the molecules are found lying flat on the surface in submonolayer coverages. We determine an elongation of the C-C bond length, for C2H2 and C2H4 on Cu(100) of 0.21(2) Å and 0.10(2) Å respectively, using the position of the σ resonance on a common energy scale with the gas phase. The results are compared with the ones of strong chemisorption on Pt(111). The σ-shape resonance of C2H6 chemisorbed on a metal substrate is reported for the first time. The molecule shows no elongation. © 1986.