Force field for the atomistic simulation of the properties of hydrazine, organic hydrazine derivatives, and energetic hydrazinium ionic liquids*

A force field (FF) is reported for hydrazine (N2H4) and organic hydrazine derivatives, including monomethylhydrazine, 1,1-dimethylhydrazine, monoethyl hydrazine, and 2-hydroxyethylhydrazine. The FF successfully reproduces a range of equilibrium properties, including vapor–liquid coexistence densities, vapor pressures, enthalpies of vaporization, and critical properties. Several dynamic properties, including self-diffusion coefficients and rotational time constants, are reported and found to be qualitatively consistent with experimental viscosities. Using this as a basis, a FF is also developed for the protonated forms of these species, i.e., hydrazinium-based cations. Properties of 1:1 energetic salts formed by pairing these cations with the nitrate anion are computed and compared with a limited amount of experimental data. The simulations indicate that the ionic liquid (IL) 2-hydroxyethylhydra zinum nitrate (2-HEHN) has significantly slower dynamics than the other hydrazinium ILs.