Development of gas-phase reaction mechanism for ammonium perchlorate using quantum mechanics calculations

The chemical kinetics involved during the initiation and subsequent reactions of ammonium perchlorate (AP) in gas phase is studied using quantum mechanics (QM) based calculations. In this study, a gas-phase reaction mechanism is formulated where-in several new initiation steps are proposed between NH₃ and HOCLO₃. The developed reaction mechanism is further compared with existing gas-phase mechanisms developed by Beckstead and his group at Brigham Young University, and additional reactions proposed by Lin and his group at Emory University. Here-in, quantum mechanics calculations were performed using Gaussian 09 program package to identify reaction pathways via transition state theory (TST). Searches for transition states were performed using density functional theory (DFT) and low-level basis-sets such as B3LYP/6-31G(d). Once a transition state with a single negative frequency was identified, intrinsic reaction coordinate (IRC) calculations were then performed to link the reactants to the products. Higher level calculations were then performed using the compound method G4(MP2) to compute the thermodynamic properties of species at equilibrium or at transition states. This work elucidates how QM can contribute to further our understanding of the complex chemical kinetics involved during the decomposition of AP in the gas phase.