Photoionization mass spectrometric study of N2H2 and N2H3: N–H, N=N bond energies and proton affinity of N2

Abstract

The photoion yield curves of N2H+2, N2H+, and H+2 from N2H2 have been studied by photoionization mass spectrometry. The adiabatic ionization potential of N2H2 determined (9.589 ± 0.007 eV) is in excellent agreement with that obtained by photoelectron spectroscopy (PES). The appearance potential of N2H+ (10.954 ± 0.019 eV at 0 K) is in good agreement with earlier electron impact measurements. The appearance potential of H+2 (<13.526 ±0.03; probably ≤13.403 ±0.036 eV, at 0 K) leads to ΔH0f0 (N2H2) >43.8 ±0.7; probably ≥46.6 ±0.8 kcal/mol. Consequently, proton affinity (PA) (N2) <121.8 ±0.8; probably ≤119.0 ±0.9 kcal/mol, which is in good agreement with results from proton transfer experiments and with most ab initio calculations. The N■N ‘‘double bond’’ energy determined from N2H2→2NH is <126.6 ±1.0; probably ≤123.8 ±1.1 kcal/mol. The adiabatic ionization potential of N2H3 is found to be 7.61±0.01 eV. This observation leads to D0 (H2NNH–H)=80.8±0.3 kcal/mol, and D0(HNNH–H)≂43.8±1.1 kcal/mol.