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

摘要

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 k1(CD3NO2)/k1(CH3NO2) = 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).