Gross- and Partial-Ionization Cross Sections for Electrons on Water Vapor in the Energy Range 0.1–20 keV

Measurements have been made on the gross-ionization cross sections for 0.1–20-keV electrons on water vapor at pressures of about 3×10−4 torr. The results are compared with the cross sections of H2 and O2. Within the experimental error of 15% we found no deviations from the additivity rule. The energy dependence of the cross section satisfies the Bethe—Fano—Platzman relation for collision-induced dipole transitions at energies exceeding 400 eV. A comparison is made with photoionization and inelastic electron-scattering cross sections. Some results are given on the partial cross sections for the production of fragment ions for 0.02–2-keV electrons on water vapor.