Clustering Reactions of the Protonated Nitrogen N2H+ with Hydrogen Molecule in the Gas Phase

Clustering reactions of the protonated nitrogen N2H+ with hydrogen molecule, N2H+(H2)n−1+H2=N2H+(H2)n(n–1, n), were studied in a pulsed electron beam mass spectrometer with a high-pressure ion source. The values of enthalpy change −ΔSn−1,n(kcal/mol) and the entropy change −ΔSn−1,n(e.u.) obtained from the van’t Hoff plots of equilibrium constants were (0, 1) 7.2, 22.6, (1, 2) 1.5, 14.0. No cluster ions larger than N2H+(H2)2 were observed even at −187 °C. The relatively low values of enthalpy change for the clustering reactions (0, 1) and (1, 2) suggest that the positive charge in N2H+ is delocalized, the N2H+ ion very weakly interacting with additional hydrogen molecules electrophilicly. The calculated entropy change also suggests that hydrogen molecules in N2H+-(H2)n are weakly bound to the core ion N2H+, having considerable freedom of motion in the cluster ion. The thermochemical study proves that the cluster ion N2H+(H2)2 does not have the structure of the protonated hydrazine N2H6+.