Absolute total electron impact ionization cross-sections have been measured for CO, CO2, OCS and CS2 from near threshold to 250 eV. Experimental data are compared with previously reported measurements and with calculations using the additivity method of Margreiter, Deutsch and Märk (DM) and the binary encounter Bethe method (BEB). Bond components to the total cross-section, previously deduced from systematic studies of perfluorocarbons, mixed halocarbons, nitriles, chlorocarbons and alcohols, have been shown to reproduce and predict maximum electron impact cross-sections to a high level of confidence. C=O and C=S bond cross-sections are now reported from the maximum cross-sections for CO2 and CS2, and shown to predict the measured maximum ionization cross-section for OCS to within 4%. The data for OCS and CS2 are shown to be in good accord with the expectations of previously derived relationships between the maximum ionization cross-section, the molecular volume polarizability and the molecular ion appearance energy (ionization threshold energy).
