Ions in Nitrogen

Abstract

${\mathrm{N}}^{+}$, ${\mathrm{N}}_{2}^{+}$, ${\mathrm{N}}_{3}^{+}$, and ${\mathrm{N}}_{4}^{+}$ ions have been identified in nitrogen gas by use of a mass spectrometer operated with the ion source in the pressure range from ${10}^{\ensuremath{-}3}$ mm Hg to 0.6 mm Hg. Appearance potentials occur at 15.5\ifmmode\pm\else\textpm\fi{}0.2 ev for ${\mathrm{N}}_{2}^{+}$, at 15.8\ifmmode\pm\else\textpm\fi{}0.3 ev for ${\mathrm{N}}_{4}^{+}$, at 22.1\ifmmode\pm\else\textpm\fi{}0.5 ev for ${\mathrm{N}}_{3}^{+}$, and at 24.2\ifmmode\pm\else\textpm\fi{}0.4 ev for ${\mathrm{N}}^{+}$; ${\mathrm{N}}_{3}^{+}$ ions thus are formed only at much higher electron energies than ${\mathrm{N}}_{2}^{+}$ but still at 2 ev less energy than ${\mathrm{N}}^{+}$. It is believed that the ${\mathrm{N}}_{4}^{+}$ is formed by the process ${\mathrm{N}}_{2}^{+}$+${\mathrm{N}}_{2}$\ensuremath{\rightarrow}${\mathrm{N}}_{4}^{+*}$ (excited vibrationally) and the ${\mathrm{N}}_{3}^{+}$ is formed by the process ${\mathrm{N}}_{2}^{+*}$+${\mathrm{N}}_{2}$\ensuremath{\rightarrow}${\mathrm{N}}_{3}^{+}$+N, where ${\mathrm{N}}_{2}^{+*}$ is an excited ion. ${\mathrm{N}}_{4}^{+}$ and ${\mathrm{N}}_{3}^{+}$ currents decrease with increasing $\frac{E}{p}$ in the source, suggesting that they may be dissociated by molecular impacts. The ${\mathrm{N}}_{4}^{+}$ ions are considerably more readily lost than the ${\mathrm{N}}_{3}^{+}$ ions. Since the formation of ${\mathrm{N}}_{3}^{+}$ must necessarily release a nitrogen atom, this process constitutes a form of dissociation of ${\mathrm{N}}_{2}$ which may account for the value of the dissociation energy of 7.38 ev found by some methods.