Formation of N2O− via Ion–Molecule Reactions in N2O

Abstract

The production of O⁻, NO⁻ and N₂O⁻ by electron impact on N₂O has been studied as a function of pressure in the range 10⁻⁶ to 5 × 10⁻³ torr, using a quadrupole mass filter. The respective linear, quadratic, and cubic pressure dependences observed for these ions and their relative signals are consistent with the following reaction sequence and cross sections: $$\mathrm{e+}{\mathrm{N}}_2\mathrm{O}\mathrm{\hspace{0.17em}\to \hspace{0.17em}}{\mathrm{O}}^{-}+{\mathrm{N}}_2,$$ $${\mathrm{O}}^{-}+{\mathrm{N}}_2\mathrm{O}\mathrm{\hspace{0.17em}\to \hspace{0.17em}}{\mathrm{NO}}^{-}+\mathrm{NO}{\text{(3\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−16}}{\mathrm{cm}}^2\mathrm{),}$$ $${\mathrm{NO}}^{-}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{N}}_2\mathrm{O}\mathrm{\hspace{0.17em}\to \hspace{0.17em}}{\mathrm{N}}_2{\mathrm{O}}^{-}\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{NO}{\text{(1\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−16}}{\mathrm{cm}}^2\mathrm{).}$$ . An alternative explanation of the data in terms of the three‐body reaction converting O⁻ to N₂O⁻ is rejected due to the implausibly large coefficient required to explain the data. No other reactions were detected. Discrepancies between the present results and those of other workers are discussed quantitatively. It is suggested that N₂O⁻ formation by the presently proposed reaction may well be endothermic, accounting for its nonappearance in systems used to study thermal energy reactions.