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)<i>n</i>

Abstract

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 k = 8 × 10−29cc2molecule−2·sec−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 k = 5 × 10−29cc2molecule−2·sec−1 and energy of activation − 1 kcal/mole or second-order dependence with k = 1.3 × 10−12cc molecule−1·sec−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 n = 1 to n = 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.