Isomer effect in the total electron impact ionization cross section of cyclopropane and propene (C₃H₆)

The Deutsch-Maerk (DM) formalism was used to calculate absolute total electron impact ionization cross sections for the two C₃H₆ isomers cyclopropane (-H₂C-CH₂-CH₂-) and propene (H₂C double bond CH-CH₃). The agreement between the calculated cross sections and the experimentally determined cross sections (Nishimura H and Tawara H 1994 J. Phys. B: At. Mol. Opt. Phys. 27 2063) is excellent in terms of the absolute magnitude for impact energies below 100 eV and satisfactory for higher impact energies. However, the DM calculation does not reproduce the slight isomer effect that was found in the experimental data: i.e. the measured ionization cross section for propene was found to be larger by a few per cent than the cross section for cyclopropane.