Absolute electron-impact ionization cross sections for a range of C-1 to C-5 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 chlo rocarbons (one to five carbon atoms), including an chlorine-substituted met hanes and ethanes. Correlations between the measured ionization cross secti on, ionization potential and molecular polarizability volume are explored a nd compared with data for the perfluorocarbons and mixed halocarbons. A C-C l bond additivity cross section determined previously for mixed halomethane s has been refined to fit the experimental data for the higher chlorocarbon s. 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-Mark and binary-encounter Bethe models.