C 1s photoionization of H2CO and C2H4: An angle-resolved photoelectron study

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Abstract
We have measured partial photoionization cross sections σ and asymmetry parameters β of the C 1s main line and the π→π* shake‐up satellites of the isoelectronic molecules formaldehyde and ethylene in the near threshold region. In all channels we observe a strong cross section enhancement and a decrease in the β parameter due to a shape resonance in the continuum. For each molecule the variation of σ and β with photoelectron kinetic energy is nearly identical for main line and satellites indicating only relatively small modifications of the effective molecular potential induced by the additional π→π* excitation. There are no indications of conjugate shake‐up processes in either molecule.