Measurements of Secondary-Electron Spectra Produced by Electron Impact Ionization of a Number of Simple Gases

The energy distribution and angular dependence of secondary electrons generated by the impact of 100–2000‐eV electrons on He, N₂, and O₂ and by the impact of 500‐eV electrons on Ne, Ar, Kr, Xe, H₂, NO, CO, H₂O, NH₃, CH₄, C₂H₂, and CO₂ have been measured over the 4–200‐eV range. The measurements were made in a crossed‐beam apparatus with the use of a fixed hemispherical electrostatic analyzer and a rotatable electron gun. The observed spectra were integrated over angle to obtain relative cross sections for secondary‐electron production. It was found that the shapes of the spectra of all the gases (except Ar, Kr, and Xe, which contain intense electron emission features in this energy range) were smooth and qualitatively similar, approaching a constant cross section at low secondary energies, and falling off at high secondary energies slightly faster than $E_s^{\text{−2}}$ , where E₈ was the energy of the secondary. The shape of the spectrum was found to be nearly independent of primary energy in He, O₂, and N₂.