Vibrational Excitation of Nitrogen by Electron Impact

The vibrational excitation of nitrogen molecules by electrons in the energy range 1.5 to 4 ev is studied using a double electrostatic analyzer. The beam of essentially monoenergetic electrons (half-width about 0.06 ev) is produced by the first analyzer and is crossed by a molecular beam of ${\mathrm{N}}_2$ in the collision chamber. The energy distribution of forward scattered electrons is analyzed in the second electrostatic analyzer. Peaks resulting from those electrons which have lost discrete amounts of energy in exciting vibrational levels up to $v=8\mathrm{}$ are observed. The energy dependence of the cross section for vibrational excitation to $v=2, 3, 4, 5, 6, 7, 8$ is obtained and pronounced structure is observed. The experiment is consistent with the hypothesis that the vibrational excitation in ${\mathrm{N}}_2$ around 2.3 ev proceeds via a temporary negative ion.