Absolute differential and integral electron excitation cross sections for atomic oxygen. 5. Revised values for the 3P→3S0 (1304 A) and 3P→3D0 (989 A) transitions below 30 eV

A new apparatus designed specifically for the study of electron scattering from unstable species at very low incident energies has been constructed and put into operation. Remeasurement of the O I 3P→3S0 (1304 A) differential and integral cross sections (DCS and ICS) at energies below 30 eV has provided new values for the DCS and ICS for this cross section as well as for the 3P → 3D0 (989 A) transition. These new values replace the cross sections reported by Vaughan and Doering (1987) which were measured in the original apparatus designed for high incident energy work. The two sets of measurements agree at incident energies 30 eV and above. However, the new values for the 3P→3S0 transition at 20 and 16.5 eV are larger than the previous measurements by a factor of 2 to 3. Extension of the work on this transition down to 13.87 eV shows that the cross section remains large to within a few eV of threshold, in agreement with the theoretical predictions of Rountree and Henry (1972) and Smith (1976). Similar behavior is observed for the 3P→3D0 (989 A) transition down to 20 eV. copyright American Geophysical Union 1988