Photoelectron spectra of acetylene with HeI, HeII, Zr Mζ, and Mg Kα radiation sources

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Abstract
Valence level photoelectron spectra of gaseous acetylene excited by HeI (21.217 eV), HeII (40.8 eV), Zr Mζ (151.4 eV) with Mg Kα (1253.6 eV) radiations have been obtained. With one exception, the 3σg band under Mg Kα excitation, all of the expected valence level excitations are observed in each case. The best measured orbital ionization potentials are 1πu (11.41 eV), 3σg (16.76 eV), 2σu (18.71 eV), and 2σg (23.65 eV). All values except that for 1πu are adiabatic values. Relative photoionization probabilities (cross sections) have been determined for each of the radiations and compared to those estimated theoretically. The low calculated cross sections for 3σg excitation with Mg Kα radiation provides an explanation for the lack of an observable band due to this ionization in the photoelectron spectrum. A prominent ’’shake‐up’’ peak is observed at 27.6 eV in both the Mg Kα and Zr Mζ excited valence shell photoelectron spectra although it is more pronounced in the former. Similarly the C1s core spectrum shows several ’’shake‐up’’ peaks which have been assigned with the aid of CNDO calculations.