Determination of the Mechanism of Decomposition of Energetic Molecules

As a prototype for more complex nitramines, the gas-phase decomposition of dimethylnitramine was studies in three laser-pyrolysis systems. Results in two of these systems, unlike those reported in the literature, indicate that a nitro-nitrite rearrangement pathway is competitive with the expected and previously invoked NNO2 bond scission. This rearrangement pathway has been obscure because it can lead to some of the same products that are yielded by the bond scission route. The principal evidence for nitro-nitrite rearrangement includes 1 Arrhenius parameters for decomposition that are two orders of magnitude too low to be consistent with simple N-NO2 bond scission as the sole rate-determining step, 2 molecular-beam, mass-spectro-metrically sampled laser pyrolysis studies that show direct detection of NO and the nitroxyl radical CH32NO. on a time scale too short to allow for the production of these substances in secondary bimolecular reactions, and 3 ab initio calculations in concurrent AFOSR-funded work that find a rearrangement pathway at slightly lower energy than that of simple bond scission. These results suggest that such rearrangement pathways may be a common feature of nitramine decomposition, as other studies have recently shown them to be for C-NO2 compounds. Keywords Propellants Nitramines Dimethylnitramine Chemical decomposition Laser pyrolysis.