HNNH3, a new possible isomer of N2H4: An ab initio study

Ab initio studies applying the 3-21G, 6-31G, and 6-31G** basis sets and also including the MP2 correction were carried out on H2NNH2, HNNH3, and the transition state of the reaction H2NNH2(DOUBLE BOND)HNNH3. First, the geometries of molecules were optimized using the theoretical methods mentioned in the restricted Hartree–Fock (RHF) scheme. The energies of the molecules corresponding to RHF/6-31G** geometries were subsequently calculated including electron-correlation effects at the level of the second-order Moller–Plesset (MP2) perturbation theory. The vibrational frequencies, net charges, and dipole moments were obtained from the theoretical calculations. The results of our calculations indicate unambiguously that H2NNH2 is thermodynamically more stable than is HNNH3. On the other hand, an isolated HNNH3 molecule once created would be stable since barriers for its unimolecular isomerization and decomposition are relatively high. But HNNH3 is unlikely to be isolated in measurable amounts because of bimolecular tautomerization. Nevertheless, HNNH3 can be considered as an intermediate in chemical processes involving N2H4. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 447–452, 1997