Energetic neutral atom (ENA) detectors have been successfully flown on missions such as the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) and are now an important tool for probing the geospace environment. Interpretation of ENA data, however, requires knowledge of a number of key charge transfer cross sections. Here we present a critical review of the published experimental measurements and recommend a set of parameterized cross sections. The processes considered are charge transfer of H+ and O+ with H, O, N2, and O2 for collision energies from 10 eV to 100 keV. The limitations of the measurement techniques and the probable reliability of the recommended cross sections are addressed.

Accurate values of the electron-impact ionization cross sections for the rare gases are needed in a variety of contexts. However, despite numerous investigations over many decades, uncertainty as to the correct values has persisted. The pioneering total-cross-section measurements of Rapp and Englander-Golden are generally regarded as the most reliable but no comprehensive study has independently verified their correctness. In this paper, measurements of electron-impact ionization cross sections of helium, neon, argon, krypton, and xenon are reported for energies ranging from the first ionization threshold to 1000 eV. These data confirm the essential correctness of Rapp and Englander-Golden's total measurements and at the same time provide a complete set of consistent absolute partial cross sections.

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Absolute electron-impact total ionization cross sections of chlorofluoromethanes Absolute partial cross sections for electron-impact ionization of NO and NO 2 from threshold to 1000 eV Absolute partial cross sections for electron-impact ionization of H 2 O and D 2 O from threshold to 1000 eV Absolute partial cross sections for the production of CH 4 ϩ , CH 3 ϩ , CH 2 ϩ , CH ϩ , C ϩ , H 2 ϩ , and H ϩ from electron-impact ionization of CH 4 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are completely collected. The overall uncertainty in the absolute cross section values is Ϯ3.5% for singly charged parent ions and is slightly greater for fragment ions. Although previous measurements are generally found to agree well with the present results for CH 4 ϩ and CH 3 ϩ , almost all previous work for the remaining fragment ions lies lower than the present results and in the case of H ϩ is lower by approximately a factor of 4.