Abstract
Ab initio molecular orbital theory at the G2 level has been used to study the energy of N2H2 and related compounds. Overall, the agreement between theory and experiment is good. The G2 enthalpy of formation ΔH0f0(N2H2) of 49.6 kcal/mol supports the experimental estimate of ≥46.6 kcal/mol derived by Ruscic and Berkowitz [J. Chem. Phys. 95, xxx4 (1991)] in a recent photoionization study. Predicted dissociation energies are D0(HN■NH)=122.8 kcal/mol, D0(HNNH–H)=43.6 kcal/mol, and D0(H2N■NH–H)=82.1 kcal/mol. The G2 value for the proton affinity (PA) of N2 at 298 K is PA298=118.1 kcal/mol. The G2 ionization potential of N2H3 of 7.54 eV is in agreement with the new value of ≤7.61 eV reported by Ruscic and Berkowitz. The G2 results for the ionization potential of N2H4 and the appearance potential of N+2 from N2H2 are in disagreement with experimental results suggesting that detection of the origins in these cases are thwarted by large geometry changes and significant Franck–Condon effects.
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