Hybridisation and vibrational excitation of C2H2 on Co(0 0 0 1)

The chemisorption of acetylene on the Co(0 0 0 1) single crystal surface has been studied using high resolution core level photoemission, X-ray absorption spectroscopy and low energy electron diffraction. At low temperatures (⩽300 K) acetylene forms a strong chemisorption bond to the substrate, creating a state of hybridisation close to sp3. The molecules are confirmed to be oriented with the C–C axis parallel to the surface. The vibrational splitting in the photoemission spectra due to excitation of the C–H stretch vibration is determined to be (389±8) meV, which is ∼6% lower then the reported C–H stretch vibration frequency for gaseous acetylene. The S-factor of the C–H-vibrational mode is determined to be (0.17±0.02), considerably higher than those reported for C2H2 adsorbed on other substrates.