Ionization Efficiency Curves of Acetylene by Electron Impact

Ionization efficiency curves have been measured for the ions including CH2+ produced from acetylene by monoenergetic electron impact over ranges of about 10 eV near their appearance thresholds. The total ionization of ficiency curve shows breaks at the energies in agreement with the ionization potentials determined by photoelectron spectroscopy. Other breaks in the curve were found to correspond to autoionizing states. The appearance potential of C2H+ almost agrees with that by photoionization mass spectrometry. The potentials of other fragment ions are not always close to those by previous electron impact experiments.