Excitation ofO2+First Negative Bands by Electron Impact onO2

Absolute cross sections for the electron-impact excitation of the ${\mathrm{O}}_2^{+}$ first negative bands were measured from threshold to 400 eV and extrapolated to 1000 eV by means of a Bethe-Oppenheimer relationship. The peak cross sections for the ($n+1, n$) and ($n+2, n$) sequences were found to be 5.30×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$±10% and 2.10×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$±10% at 100 eV, respectively. The cross sections for the (0,0) and (1,0) bands had a maximum value of 2.14×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$±15% and 4.33×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$±15%, respectively. The ratio of the total ionization cross section of ${\mathrm{O}}_2$ to the excitation cross sections of the first negative bands was nearly constant over the energy range 30-1000 eV; it had an average value of 64 for the (1,0) band. The lifetime of the ${\nu }^{\prime }=1\mathrm{}$ level of the $b^4{\Sigma }_g^{-}$ state was found to be 1.19 μsec±5%.