Hydrated Positive Ions in Nitric-Oxide-Water Afterglows

Results of measurements performed on a stationary NO-${\mathrm{H}}_2$O afterglow are reported in this paper. The gas mixture was contained in a large, gold-plated, cylindrical chamber in which the NO was ionized by means of krypton resonance radiation. The ions from the afterglow were sampled through an electrically insulated orifice and were quantitatively detected by time-resolved mass spectrometry. For N${\mathrm{O}}^{+}$ ions reacting in NO-${\mathrm{H}}_2$O mixtures at 295 K, the product-ion mass spectrum is dominated by N${\mathrm{O}}^{+}$ and its hydrates, $\mathrm{N}{\mathrm{O}}^{+}·n{\mathrm{H}}_2\mathrm{O}$, and by hydrated hydronium, ${\mathrm{H}}_3{\mathrm{O}}^{+}·n{\mathrm{H}}_2\mathrm{O}$. The sequence of reactions leading to these products has been determined, and the rate constant for the three-body conversion of N${\mathrm{O}}^{+}$ to N${\mathrm{O}}^{+}$·${\mathrm{H}}_2$O has been measured to be (1.5 ± 0.5)×1$0^{-28\mathrm{}}$ ${\mathrm{cm}}^6$/sec. Bounds for several other rate constants in the reaction sequence have been obtained. The ions ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$·2${\mathrm{H}}_2$O, ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$·3${\mathrm{H}}_2$O, and ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$·4${\mathrm{H}}_2$O observed in the afterglow are of the same family as the hydronium ion ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$ and its hydrates ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$·${\mathrm{H}}_2$O and ${\mathrm{H}}_3$ ${\mathrm{O}}^{+}$·2${\mathrm{H}}_2$O, which are prominent in the $D$ region of the ionsphere. Reaction sequences similar to the one reported in this paper, which involve multiply hydrated atmospheric ions, may be an important contributors to the production of the hydrated hydronium observed in the ionosphere.