Kinetic study of the combustion of organophosphorus compounds

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The thermochemistry and kinetics of organophosphorus compounds were studied, with BAC-MP4 method estimations as a basis and PM3 semi-empirical estimations for many new compounds. New group additivity values were proposed for enthalpies of formation at 298 K, and entropies and heat capacities of species involving pentavalent phosphorus bonded to carbon, hydrogen, oxygen, fluorine, nitrogen, and sulfur atoms. The kinetic features of unimolecular elimination were investigated by modeling pyrolysis experiments of dimethyl ethyl phosphonate (DEMP), triethyl phosphate (TEP), and di-isopropyl methyl phosphonate (DIMP). Rate constants were proposed for four- and six-center eliminations. A new combustion mechanism was developed in a systematic and comprehensive way and involved 41 phosphorus compounds in 202 reactions. All possible intermediates were taken into account. This reaction mechanism was applied to the modeling of H2/O2 flames doped with dimethyl methyl phosphonate (DMMP) and trimethyl phosphate (TMP), which are chemical warfare surrogates. The promoting effect of the agent and the species profiles were correctly reproduced. The decomposition reaction channels were studied: they included radical reactions and molecular eliminations. The cause of the increase of the reactivity of the flame was attributed to some radical combination cycles leading to an increase of heat release, which enhances the global reaction rate in spite of the radical concentration drop.