Absolute differential and integral electron excitation cross sections for atomic oxygen, 6, the ³P → ³P and ³P → 5P transitions from 13.87 to 100 eV

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We report the absolute differential and integral cross sections of the forbidden atomic oxygen ³P → ³P, 10.99 eV, and ³P → 5P, 10.76 eV, transitions for incident electron impact energies of 13.87 to 100 eV. These measurements are an extension of excitation cross section results that were reported previously at 30 eV incident energy by Gulcicek and Doering (1987). The differential cross sections (DCS) for the ³P → ³P transition are forward peaked, although not as strongly as for an electric dipole allowed transition and became flatter at the lower incident energies. The DCS for the ³P → 5P transition is roughly isotropic with scattering angle at all incident energies. The agreement between the ³P → ³P direct integral excitation cross sections (ICS) and the experimental 8446 Å emission cross section of Zipf, adjusted to remove cascade, is good over the entire energy range studied. The agreement with some, but not all, previous theoretical calculations for both transitions is satisfactory. The worst disagreement, roughly a factor of 2, is at the lowest incident energy, 13.87 eV, where the experimental results suggest that the ICS has begun to decrease toward threshold while the theoretical calculations show a continued increase. The ratio of the ICS for the ³P → ³P to the ³P → 5P transition varies from >6 at energies >30 eV to 2.2 at 13.87 eV. These ratios, which correspond directly to the 8446 Å/7774 Å emission line ratio in the thermosphere, allow conclusions to be drawn about the exciting electron energy distribution from the emission intensity ratio.