Computational study of decomposition mechanisms and thermodynamic properties of molecular-type cracking patterns for the highly energetic molecule GZT

Abstract

This study uses the Gaussian 03 program and density functional theory B3LYP with three basis set methods-[B3LYP/6-311+G(d,p), B3LYP/6-31+G(2d,p), and B3LYP/6-31G(d,p)]-to model the highly energetic ionic compound diguanidinium 5,5'-azotetrazolate (GZT) to research its decomposition mechanisms and thermodynamic properties. Molecular-type cracking patterns are proposed, which were initiated by heterocyclic ring opening, sequential cracking of the two five-membered rings of GZT, and simultaneous release of N2 molecules; whereas proton transfer, bond-breaking, and atomic rearrangements were performed subsequently. Finally, 15 reaction paths and five transition states were obtained. All possible decomposition species and transition states, including intermediates and products, were identified, and their corresponding enthalpy and Gibbs free energy values were obtained. The results revealed that (1) the maximum activation energy required is 187.8 kJ mol(-1), and the enthalpy change (ΔH) and Gibbs free-energy change (ΔG) of the net reaction are -525.1 kJ mol(-1) and -935.6 kJ mol(-1), respectively; (2) GZT can release large amounts of energy, the main contribution being from the disintegration of the 5,5'-azotetrazolate anion (ZT(2-)) skeleton (ΔH = -598.3 kJ mol(-1)); and (3) the final products contained major amounts of N2 gas, but remaining gas molecules such as HCN and NH3 were obtained, which are in agreement with experimental results. The detailed decomposition simulation results demonstrated the feasibility of this method to calculate the energies of the thermodynamic reactions for the highly energetic GZT and predict the most feasible pathways and the final products.