Ionization of water and carbon dioxide molecules by electron impact near threshold

A measurement technique is described and relative cross-sections for direct and dissociative ionization of H2O and CO2 molecules by electron impact near the threshold are obtained. The experiment is performed by a setup with mass separation of the ions by a monopole mass spectrometer and their detection by a secondary electron multiplicator. The energy dependencies of the cross-sections for the formation of the main molecule ions and fragment ions resulting from dissociation are given in the incident electron energy range from 7 to 35 eV.