Absolute optical-emission cross sections have been measured for transitions in the wavelength range 3690–11 300 Å originating from 32 terms of excited oxygen atoms produced by electron impact on oxygen molecules with incident electron energy up to 500 eV. The excitation functions show a broad peak at about 90 eV with a shoulderlike structure of varying degree near 35 eV. The observed threshold energy is very close to the energy defect of the dissociation process. Near the threshold, dissociative excitation through partly bound Rydberg states of the oxygen molecule is believed to be a major mechanism for producing the observed atomic-oxygen emission, whereas simultaneous ionization and excitation followed by dissociation become important at energies above 50 eV. Combination of the measured cross sections with theoretical transition probabilities allows us to determine the absolute optical-emission cross sections for a series of atomic-oxygen transitions in the long-wavelength infrared region of the spectrum.

• Received 11 July 1985

DOI:https://doi.org/10.1103/PhysRevA.32.2100