A study of the infrared emission from the O I (3d 3D0) and (4s 5S0) states produced by electron impact excitation of O2

We have measured the absolute emission cross section value for the O i(3p 3P–3d 3D0, λ=11 287 Å) and the (3p 5P–4s 5S0, λ=11 299 Å) multiplets excited by electron impact on O2. The former cross section has a value of 3.05×10−19 cm2±15% at 100 eV, while the latter’s value is 4.14×10−19 cm2±15%. The quintet emission at λ=11 299 Å is the only deexcitation channel for the 4s 5S0 state, and, therefore, represents the total excitation cross section for that state. However, the λ=11 287 Å branch from the O i(3d 3D0) state only constitutes ∼25% of the total 3d 3D0 cross section, with the major branch from this state being the transition to the ground state observed at λ=1027 Å. The branching ratio obtained in this study is in good agreement with the theoretical calculation of Pradhan and Saraph (ω̃11 287=0.28), but our absolute σ(λ=11 287 Å) value is substantially smaller than the result reported recently by Schulman et al.