Absolute Fluorescence Yields of 3914-Å Photons fromN2and Air Excited by Relativistic Electrons

The absolute fluorescence intensity of the first negative (0, 0) band of ${\mathrm{N}}_2^{+}$ at 3914 Å excited by bombardment of ${\mathrm{N}}_2$ and ${\mathrm{N}}_2$: ${\mathrm{O}}_2$ mixtures with electrons in the previously unstudied energy range 0.65 to 1.6 MeV has been measured at gas pressures of 0.05 to 8 Torr. An effective cross section for the production of these photons by 1.5-MeV primary electrons and all secondary electrons resulting from the ionization events is found to be (1.6 ± 0.4) × ${10}^{-19\mathrm{}}$ ${\mathrm{cm}}^2$. The measurements indicate that 10% of the ${\mathrm{N}}_2^{+}$ ions are formed in the $B{}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}(v^{\prime }=0)$ state and that the fluorescence efficiency for the 3914-Å band is (6.0 ± 1.9) × ${10}^{-3\mathrm{}}$ for ${\mathrm{N}}_2$ and (4.8 ± 1.5) × ${10}^{-3\mathrm{}}$ for air, in agreement with modern results at lower energies. From comparison with recent published results of primary excitation at lower energies, it appears that $\frac{2}{3}$ of the observed photons are produced by secondary electrons. Quenching cross sections for the $B{}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}(v^{\prime }=0)$ state of ${\mathrm{N}}_2^{+}$ in collisions with ground-state neutral molecules of ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ have been found to be (6.5 ± 0.4) × ${10}^{-15\mathrm{}}$ and (10.9 ± 4.5) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$, respectively.