Oscillator strength and electron-impact excitation of the Schumann-Runge continuum of the oxygen molecule

By using the method of multiconfiguration self-consistent field, the electronic wave functions for the $X{}_{}{}^3{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}$ and $B{}_{}{}^3{}_{}{}^{}\Sigma _u^{-}{}_{}{}^{}$ states of ${\mathrm{O}}_2$ are determined for twelve values of internuclear distances. From the appropriate electronic-vibrational functions, the oscillator strengths for the $X{}_{}{}^3{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}\to B{}_{}{}^3{}_{}{}^{}\Sigma _u^{-}{}_{}{}^{}$ absorption (Schumann-Runge) continuum are calculated over the energy range of 7-9.5 eV. The results are in good agreement with experiments except at the high-energy edge (above 9 eV) which corresponds to the very steeply varying part of the potential curve. A calculation of the electron-impact excitation cross sections for the $B{}_{}{}^3{}_{}{}^{}\Sigma _u^{-}{}_{}{}^{}$ state with the Born-Ochkur approximation is also reported for incident electron energy up to 1000 eV.