Excitation Functions of the Auroral Bands ofN2+and the Comet-Tail Bands of CO+, Excited by Electron Impact

The excitation functions of the auroral bands of $\mathrm{N}_2^{}{}_{}{}^{+}$ and the comet-tail bands of C${\mathrm{O}}^{+}$, excited by electron impact, have been determined by the method of photographic intensitometry. A discharge tube is described in which electrons were accelerated from three filaments into the inside of a hollow cylindrical grid where the discharge took place. The discharge tube was operated at a pressure of 0.001 mm Hg with an electron current of 25 ma. The mean free path of the electrons was large in comparison to the interelectrode distances. It was found by probe electrode measurements that the "transparency" of the grid to electrons from the filaments diminished with the voltage for voltages less than 150 volts. Because of this effect it was necessary to correct the intensity measurements to correspond to a constant excitation current.