Abstract: Two fully optimized geometries of hydrazinium nitroformate(HNF) ion pairs have been obtained with DFT method at the B3LYP/6-31+G^** level. The binding energies of ion pairs are corrected for the basis set superposition errors(BSSE) and for the zero-point energies(ZPE). The corrected binding energy of the most stable ion pair is predicted to be -420.03 kJ/mol, which can compensate for the totaLIonization energy needed for the ionization of hydrazine and trinitromethane. The intermolecular bonds between ion pairs primarily consist of Coulomb interaction and, judged by the electron densities at the bond critical points, the covalent interactions also make a remarkable contribution to the bonding. Based on statistical thermodynamics, the thermodynamic properties of the related systems have been calculated. The changes of the enthalpy and Gibbs free energy on going from the ions to the most stable ion pair are predicted to be -419.72 and -376.61 kJ/mol at 298.2 K, respectively.

Key words: Hydrazinium nitroformate(HNF), Ion pair, Intermolecualr interaction, DFT method, Thermodynamic properties