Absolute electron-impact ionization cross sections for a range of C₁ to C₅ chlorocarbons

Absolute total electron-impact ionization cross sections from threshold to 220 eV are reported for the formation of positive ions from a range of chlorocarbons (one to five carbon atoms), including all chlorine-substituted methanes and ethanes. Correlations between the measured ionization cross section, ionization potential and molecular polarizability volume are explored and compared with data for the perfluorocarbons and mixed halocarbons. A C-Cl bond additivity cross section determined previously for mixed halomethanes has been refined to fit the experimental data for the higher chlorocarbons. Maximum cross sections predicted using bond additivity contributions are shown to be in agreement with experiment for a wide range of molecules to better than ±10% accuracy, and in most cases to better than ±5%. The experimental data are compared with the predictions of the Deutsch-Märk and binary-encounter Bethe models.