The decomposition mechanism of guanidium nitrate (GN) was investigated by quantum chemistry calculations. Optimized structures of reactants, products, and transition states were obtained at the ωB97X-D/6-311++G(d,p)/SCRF = (solvent = water) level of theory and the total electron energies and free energies of these structures were calculated at the CBS-QB3 level of theory. In the initial decomposition pathway of GN, two mechanisms occur in parallel: CN3H5 decomposition and the interaction between CN3H5 and HNO3. The former mechanism has three pathways and each of these schemes provided the same global reaction: CN3H5→ HNCNH + NH3. Pathways for neutral monomolecular decomposition, neutral-neutral bimolecular decomposition (CN3H5 + CN3H5), and cation-neutral bimolecular reaction (CN3H6+ + CN3H5) were developed. The latter reaction has four pathways and each of these schemes provided the same global reaction: CN3H5 + HNO3 → HNCNH + N2O + 2H2O. These schemes can be divided according to the combination of oxidizers (HNO3 or N2O5) and reductants (CN3H5 or CN3H6+). Based on the energy-barrier results, HNO3-catalyzed monomolecular decomposition in CN3H5 decomposition and N2O5/CN3H5 schemes in the interaction between CN3H5 and HNO3 are the most plausible mechanisms.
guanidine nitrate, gas-generation agent, decomposition, liquid-phase reaction, ab initio calculation