Correlation effects in the ionization of hydrocarbons

The spectral intensity for ionization as a function of binding energy for the valence electrons of ethylene, allene, butatriene, trans-butadiene, acetylene, benzene, methane, ethane, and cyclopropane is computed by a many-body Green's function method. The results are used to interpret unidentified structures in experimental ionization spectra. For the ionization out of the inner valence orbitals of the unsaturated molecules the spectral intensity is found to be distributed over several lines, in sharp contrast to the ionization out of the inner valence orbitals of the saturated molecules where the greater part of the intensity appears in one main line. The reasons for this behavior are discussed. It is also found that there is a correspondence between the behavior of the spectral intensity in the inner valence region and the satellite structure in the outer valence region. For C₆H₆, C ₄H₄, and C₄H₆ interesting satellite lines of considerable intensity are predicted to be situated in the outer valence region accessible with Hei radiation.