Absolute experimental differential and integral electron excitation cross sections for atomic oxygen: 2. The (³P → ³S°) transition (1304 Å) from 16.5 to 200 eV with comparison to atomic hydrogen

Abstract

Previously reported measurements of the absolute experimental electron excitation cross section for the O (³P → ³S°) transition (1304 Å) at 100 eV have been extended to a wide range of incident energies from 16.5 to 200 eV. Both the O I and H I (n = 2) cross sections were measured simultaneously, and the H I (n = 2) cross sections were compared with previous results as a test of experimental reliability. The O I differential cross sections vary smoothly with incident energy and are flatter with scattering angle at the lower incident energies, as expected. The absolute integral cross section is found to agree with the theoretical shape and magnitude at higher energies. Comparison is made between fluorescence cross sections of Zipf and Erdman and present direct electron excitation cross sections. At low energies the direct excitation cross section is roughly 50% of the fluorescence cross section, suggesting that the cascade contribution to 1304‐Å fluorescence from excitation of the 2³P and other states is about the same magnitude as direct excitation. Generalized oscillator plots of the 100‐, 150‐, and 200‐eV data demonstrate the applicability of the Born approximation. Present results for the H I (n = 2) integral cross sections agree with previous results within 15%.