Two‐Photon Spectroscopy of Acetylene ‐ Photodissociation Processes at 9‐10 eV Energy Levels

The gerade states of acetylene at 9‐10 eV have been studied by monitoring the C₂ emission. Larger Δv₂ excitations are seen than previously reported by Ashfold et al. The observed two‐photon resonant levels show extensive predissociation. Experimental evidence from the two‐color photofragment excitation measurement is given to support the conclusion that the excited‐state ethynyl radical and atomic hydrogen are the corresponding predissociation products. Most C₂ emissions seen in this work are due to the subsequent photodissociation of the intermediate C₂H to C₂ (d³Π_g).