Electron-impact excitation of the 3S and 5S states of atomic oxygen

Absolute cross sections for the excitation of the OI 3s(3S0) and 3s(5S0) states by electron impact on atomic oxygen have been measured for electron energies from threshold to 300 eV. The magnitude of the 3S0 cross section is 5.3×10−17 cm2±40% at its peak at 20 eV. This cross section differs in magnitude and shape from the result reported earlier. The 5S0 cross section has a maximum value of 2.5×10−17 cm2±50% at 15 eV. Both cross sections are larger than the values predicted by recent theoretical calculations. The experimental techniques used in the production of atomic oxygen and in the measurement of the OI density have been improved and are described in detail. Critical experimental problems concerning the loss of atoms at the system walls and the role of excited states of O2 in the discharged gas are also discussed.