[en] Effective cross sections for excitation of atomic oxygen by 600--3000 eV electrons were obtained for the OII 4351.3 A spectral line corresponding to the 3p'²D/sub 5;2/⁰ →3s'²D/sub 5;2/ transition and the OII 4414.9 A and OII 4417.0 A lines of the 3p²D⁰→3s²P multiplet. Oxygen atoms were produced in the absence of O₂ molecules by the N+NO→N₂+O titration reaction. To minimize O atom recombination and elastic scattering of the electron beam, the N₂--O gas mixture was expanded into a vacuum chamber resulting in a free jet flow. This provides a unique technique for excitation cross section measurements of free radicals and reactive gases