Vibrational Excitation ofN2, CO, andH2by Electron Impact

The cross section for vibrational excitation of ${\mathrm{N}}_2$, CO, and ${\mathrm{H}}_2$ by electron impact is measured using a double electrostatic analyzer. Electrons are examined after scattering from the molecules at an angle of 72 deg. Both ${\mathrm{N}}_2$ and CO exhibit a small vibrational cross section to the first state below 1.7 and 1.0 eV, respectively, which is attributed to direct excitation by electron impact. Above these energies, many vibrational states are excited and the cross section becomes large; it is postulated that the excitation proceeds via a compound state of ${\mathrm{N}}_2$ and CO. The peak of the cross section occurs at 2.3 eV in ${\mathrm{N}}_2$ and 1.75 eV in CO. In hydrogen, the cross section to the first vibrational state predominates; the cross section to the second vibrational state of ${\mathrm{H}}_2$ is about 14% of the first state, at an energy of 3.4 eV.