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Untangling the Reaction Mechanisms Involved in the Explosive Decomposition of Model Compounds of Energetic Materials

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Final rept. 1 Sep 2013-31 May 2014

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We investigated the electron- and photon- 10.5 eV induced decomposition of nitromethane CH3NO2 in the condensed phase at 5 K. Infrared spectroscopically, we identified four newly formed molecules in irradiated D3-nitromethane ice films CH3ONO, H2CO, NO, and HNO. The data analysis suggest first order kinetics of the formation of methyl nitrite CH3ONO via isomerization of nitromethane CH3NO2 k1. Both the methyl radical and the nitrogen dioxide formed via the carbon-nitrogen bond rupture are trapped within the matrix cage and recombine back to nitromethane CH3NO2 or form methylnitrite CH3ONO. The isomerization of D3-nitromethane is faster than of nitromethane with k1CD3NO2k1CH3NO2 2.0 - 0.8 proposing non-equilibrium reaction dynamics. Methylnitrite CH3ONO decomposed via two competing pathways into formaldehyde H2CO plus nitrosyl hydride HNO and the methoxy radical CH3O plus nitrogen monoxide NO. The dominance of the molecular product channel is quite distinct from the gas phase experiments depicting a prevailing radical channel. Reflectron time-of-flight mass spectroscopy coupled to single photon ionization revealed that the reaction mechanisms in the condensed phase are more complex than in the gas phase. These involve addition of suprathermal hydrogen atoms leading eventually to H2NOH, radical-radical recombination reactions CH3NO, and pathways leading to hydroxymethylamine CH3NHOH.

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  • Physical Chemistry
  • Explosions

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