Ion–Molecule Reactions in Pure Nitrogen and Nitrogen Containing Traces of Water at Total Pressures 0.5–4 torr. Kinetics of Clustering Reactions Forming H+(H2O)n

The ion–molecule reactions in pure nitrogen and nitrogen containing traces of water were studied with a pulsed electron‐beam mass spectrometer having a field‐free high‐pressure source. The reaction N₂⁺+2N₂ = N₄⁺+N₂ occurring in pure nitrogen was found to have a third‐order rate constant ${\text{k\hspace{0.17em}=\hspace{0.17em}8\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−29}}{\mathrm{cc}}^2{\mathrm{molecule}}^{\text{−2}}·{\sec }^{\text{−1}}$ at 300°K and a negative temperature coefficient corresponding to an “activation energy” of − 2 kcal/mole at pressures up to 3.5 torr. The results for the reaction N⁺+N₂→N₃⁺, investigated under the same conditions, indicated either third‐order dependence with ${\text{k\hspace{0.17em}=\hspace{0.17em}5\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−29}}{\mathrm{cc}}^2{\mathrm{molecule}}^{\text{−2}}·{\sec }^{\text{−1}}$ and energy of activation − 1 kcal/mole or second‐order dependence with ${\text{k\hspace{0.17em}=\hspace{0.17em}1.3\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−12}}{\mathrm{cc\; molecule}}^{\text{−1}}·{\sec }^{\text{−1}}$ with no temperature coefficient. The reaction mechanism in nitrogen in the torricelli range containing water vapor in the millitorr range was found to proceed by the following reaction sequence: N₂⁺→N₄⁺→H₂O⁺→H₃O⁺→H⁺(H₂O)₂→H⁺(H₂O)_n. The rate constants for all reactions were determined. The clustering reactions H⁺(H₂O)_n+H₂O=H⁺(H₂O)_n+1 were found to be third order for $\text{n\hspace{0.17em}=\hspace{0.17em}1}$ to $\text{n\hspace{0.17em}=\hspace{0.17em}4}$ and all approximately equal to 3 × 10⁻²⁷ cc² molecule⁻²·sec⁻¹. Equilibrium constants for the clustering reactions and the rate constants for the reverse reactions were also obtained.