Photoelectron energy distribution curves from sohd acetylene were measured for exciration energies up to 30 eV using synchrotron radration Tbc partial cross sections are dtscussed m relation to theory and other experiments. The Ilru valenceband cross section shows a pronounced autoionization resonance with a shoulder and a peak 2.5 and 5.0 eV above the vacuum level. This ongutares from the resonant decay of the 20, --t 19 valence excitation (discrete shape resonance). 1 _ Introduction Studies of molecular photoemission cross sections over extended energy regions have enhanced our rmderstanding of final-state effects generally and have stimulated a fruitful and intense competition between theory and experiment in elucidating the dynamics of the photoionization process [l] _ In this general area, photoemission from ace-flene (C2H2) has been the subject of a number of recent studies [2-S] _ Experimentally, in the gas phase a sharp mmimum in the partial cross section of the In, level has been observed at hv = 14 eV, a few eV above threshold. Different explanations involving two transitions have been suggested for the resulting two-peak structure [3-71. However, in a recent calculation including electron correlation effects, the cross-section data and the minimum observed in the photoemission asymmetry parameter for the lnu photo-* Work supported in part by Bundesministerium fiir Forschung und Technologie (BMFTJ from Funds for Research with Synchrotron Radiation.