Angle-resolved photoelectron spectra of ethylene as a function of photon energy using synchrotron radiation

As a test of the applicability of multiple-scattering theory to an unsaturated organic system, angle-resolved photoelectron spectra of the first four bands of ethylene have been measured from 1.5 eV above threshold to a photon energy of 28 eV. The results are compared to the multiple-scattering theory calculations of Grimm. The comparisons are excellent except for the 1 b_3u orbital below 14 eV, and the disagreement is attributed to the occurrence of autoionization. It is found that the π orbital has a much higher β value than the σ orbitals, but the β value for the π orbital varies more rapidly than that for the σ orbitals from threshold to ～0.5 Rydberg (～7 eV).