Cross Section for Electron-Impact Excitation of the (0,0) First Negative Band ofN2+from Threshold to 3 keV

The cross section for the excitation of the (0, 0) first negative band of ${\mathrm{N}}_2^{+}$ by electron impact has been measured, using photon-counting techniques, in the energy range from threshold to 3 keV and extrapolated to 10 keV by means of a Bethe-Oppenheimer relation. In order to avoid polarization effects, the primary measurements were made at the "magic angle" of 54° 44′; complementary measurements at 90° were also obtained for comparison purposes. The excitation cross section for the (0, 0) band reached its maximum value at an energy of about 100 eV where it was (1.74 ± 0.17) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$. The ratio of the total ionization cross section to the excitation cross section was nearly constant over the energy range from 30 eV to 10 keV, and had a value of 14.1.