Ionization of Nitrogen and Oxygen Molecules by Nitrogen and Oxygen Molecules

The ionization cross sections for ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ molecules on impact with ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ molecules have been measured over the laboratory energy range from 20 to 1000 eV. The incident molecular beams were produced by the technique of ionization by electron impact, electrostatic acceleration, and neutralization by charge transfer. The measurements were carried out in a low-pressure parallel plate ionization chamber. Particular attention was paid to the problem of secondary electrons. Ionization was observed a few eV above threshold for all combinations. Cross sections which were obtained ranged from ${10}^{-20\mathrm{}}$ to 5×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$. The ${\mathrm{N}}_2$-${\mathrm{O}}_2$, ${\mathrm{O}}_2$-${\mathrm{N}}_2$, and ${\mathrm{O}}_2$-${\mathrm{O}}_2$ curves of cross section vs incident particle energy showed no apparent structure, as contrasted with ${\mathrm{N}}_2$-${\mathrm{N}}_2$ case. The ${\mathrm{N}}_2$-${\mathrm{O}}_2$ and ${\mathrm{O}}_2$-${\mathrm{N}}_2$ results were in agreement when corrected to center-of-mass energy.