These studies combine crossed laser-molecular beam scattering, velocity map imaging and computation to study the thermal decomposition mechanisms of geminal dinitro energetic materials. In our experimental studies, we photolytically generate two key intermediates in the decomposition of such energetic materials, 2-nitro-2-propyl radical and 2-nitropropene by photodissociating 2-bromo-2-nitropropane at 193 nm. These intermediates were produced at high internal energies and access a number of competing unimolecular dissociation channels. The scattering and imaging experiments provided evidence for four photodissociation pathways of 2-bromo-2-nitropropane along with a total of twelve subsequent dissociations of the resulting intermediate. In addition to the experimental studies, extensive calculations were conducted at the G4//B3LYP/6-311++g(3df,2p) level to compute the energetics of these dissociation events. Interestingly, a novel transition state (TS) for NO loss was discovered for the 2-nitro-2-propyl radical, which has a reaction barrier substantially lower than a traditional nitro-nitrite isomerization mechanism would suggest. This pathway is only available to nitroalkyl radicals and is extremely exothermic. To confirm the presence of this novel TS in a real-world system, the potential energy surface (PES) of a new energetic material, 1,1-diamino-2,2-dinitroethene (FOX-7), was calculated. This PES confirms the presence of the novel NO loss TS in FOX-7; this new TS allows for a low energy pathway to the production of NO in the unimolecular decomposition of FOX-7. In addition, these calculations demonstrate that initial loss of NO is competitive with simple C-N bond fission in unsaturated energetic materials. This low barrier and high exothermicity may be responsible for the extensive NO production and energy release observed in energetic materials with geminal dinitro groups.
|Advisor:||Butler, Laurie J.|
|Commitee:||Butler, Laurie J., Mazziotti, David A., Sibener, Steven J.|
|School:||The University of Chicago|
|School Location:||United States -- Illinois|
|Source:||DAI-B 75/07(E), Dissertation Abstracts International|
|Subjects:||Molecular chemistry, Chemistry, Physical chemistry|
|Keywords:||Energetic materials, Photodissociation, Radicals|
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