First-Principles-Based Reaction Kinetics for Decomposition of Hot, Dense Liquid TNT from ReaxFF Multiscale Reactive Dynamics Simulations

The reaction kinetics of the thermal decomposition of hot, dense liquid TNT was studied from first-principles-based ReaxFF multiscale reactive dynamics simulation strategy. The decomposition process was followed starting from the initial liquid phase, decomposition to radicals, continuing through formation of carbon-clusters products, and finally to formation of the stable gaseous products. The activation energy of the initial endothermic decomposition rate and the subsequent exothermic reactions were determined as a function of density. Analysis of fragments production in different densities and temperatures is presented. We find that unimolecular C-N bond scission dominates at the lower densities (producing NO2), whereas dimer formation and decomposition to TNT derivatives and smaller gaseous fragments prevails at higher compressions. At higher densities, enhanced carbon-clustering is observed, while the initial gaseous fragments formation is suppressed. Increasing the temperature speeds up the production of both clusters and gaseous products. The activation energy for the initial close decomposition stage of ambient liquid TNT is similar to 36 kcal/mol, close to the measured value (similar to 40 kcal/mol). This value is similar to 25 kcal/mol lower than the corresponding gas phase C-N bond scission. Finally, we suggest a simple linear growth kinetic model for describing the clustering process, which provides very good agreement with simulation results.