Abstract
Total electron impact ionization cross sections for CH4, C2H4, C2H6, C3H6 (cyclo-propane and propene) and C3H8 were determined in the energy range from threshold to 3 keV. Results are compared with the available data. The measured cross sections are found to correlate strongly to the total electron number and the molecular dipole polarizability. In connection with the total number of molecular electrons and the molecular dipole polarizability, two scaling methods for the total ionization cross sections are presented. The isomer effect is also discussed.