Atomic oxygen 3P → 3S0 (λ1304Å) transition revisited: Cross section near threshold

Abstract

The direct excitation cross section for the atomic oxygen 3P → 3S0 transition (λ1304Å) has been measured at four incident energies between 13.4 and 40 eV. These measurements were made to add sufficient detail to previous direct excitation measurements to allow the near‐threshold cross section to be determined. Previous optical measurements of the 1304Å emission cross section disagree by up to a factor of 2 in this important energy region. We have also compared the atomic hydrogen e + H(1s) → H(2s + 2p) cross section, used previously as a secondary standard for our direct excitation measurements of atomic oxygen cross sections, to recent measurements of the total e + H → Lyman alpha cross section and have found agreement at the ±15% level, making a revision of our previously reported atomic oxygen cross sections unnecessary. The new direct excitation atomic oxygen cross section results, combined with previous measurements, support the emission cross section measured by Stone and Zipf [1974] and revised by Zipf and Erdman [1985] over the measurement of Wang and McConkey [1992]. Except for the region just above threshold at 10–25 eV incident energy, all the cross section measurements now agree to within ±20%. The 100 eV value of the atomic oxygen 3P → 3S0 emission cross section from a combination of the emission and direct excitation cross section experiments is 8.6 ± 11% × 10−18 cm2.