Negative-Ion–Molecule Reactions in N2O

Abstract

The relative concentrations of various negative ions present following electron attachment to N₂O have been measured as a function of pressure. The ions were identified using a quadrupole mass spectrometer coupled to a drift tube operating at pressures between 0.3 and 8 torr. The dependence on $\mathrm{E\hspace{0.17em}/\hspace{0.17em}p}$ of the total negative‐ion current is consistent with the change from a three‐body to a two‐body attachment process at $\mathrm{E\hspace{0.17em}/\hspace{0.17em}p}$ values near 1 V cm⁻¹·torr⁻¹. Using purified N₂O at $\text{E\hspace{0.17em}/\hspace{0.17em}p\hspace{0.17em}=\hspace{0.17em}10}{\mathrm{V\; cm}}^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ , the O⁻ ions formed by attachment undergo a series of ion–molecule reactions with the N₂O to form ions with masses corresponding to NO⁻, N₂O₂⁻, NO₂⁻, and N₃O₂⁻. Several reaction schemes are considered, and a fit to the observed pressure dependence is obtained by postulating the presence of intermediate excited states of N₂O₂⁻ and N₃O₂⁻ with lifetimes of 4 × 10⁻⁷ and 10⁻⁷ sec.