Vibrational Excitation ofO2by Electron Impact above 4 eV

Vibrational excitation of ${\mathrm{O}}_2$ by electrons in the energy range 4-15 eV is studied with a crossed-beam double electrostatic analyzer. The differential vibrational cross sections for $v=1-4\mathrm{}$ at 25° show a bell-shaped energy dependence peaked near 9.5 eV. The observations are interpreted in terms of resonant contributions by excited states of ${\mathrm{O}}_2^{-}$. There is also evidence for the resonant enhancement of electronic excitations.