Angular dependent photoelectron spectral measurements for acetylene

The photoelectron angular distributions of acetylene have been obtained using 584 Å light. The π asymmetry parameter β of the CC triple bond is lower by 0.2 than the corresponding parameter of the CC double bond in ethylene. The β values of the π ionization and the second σ ionization are very close to each other indicating that the rule that π ionizations exhibit significantly higher β values than σ iomzations in unsaturated hydrocarbons is of limited utility here.