Photoemission Observations of π-d Bonding and Surface Reactions of Adsorbed Hydrocarbons on Ni(111)

Ionization energies for chemisorbed acetylene, ethylene, and benzene exhibit π-orbital bonding shifts (∼ 0.9-1.5 eV) as well as large nonchemical-bonding relaxation shifts of ∼ 1-3 eV for both π and σ orbitals. Dehydrogenation of chemisorbed ethylene to acetylene for TA230A°K is directly observed. We estimate π-d bonding interaction strengths and chemisorption energies from spectroscopic energy levels and predict that this surface reaction becomes exothermic because of π-d bonding. © 1974 The American Physical Society.