Use of Laser-Powered Homogeneous Pyrolysis to Determine the Initial Steps in the Homogeneous Gas-Phase Decomposition of Cyclic Nitramines

摘要

As a prototype for more complex nitramines, the gas-phase decomposition of dimethylnitramine has been studied experimentally in two different laser-pyrolysis systems and theoretically using ab initio quantum mechanical calculations. Our studies, unlike those reported in the literature, indicate that a nitro-nitrite rearrangement pathway is competitive with the expected (and previously invoked) N-NO2 bond scission. This rearrangement pathway has been obscure because it can lead to some of the same products as are yielded by the bond scission route. The principal evidence for nitro-nitrite rearrangement is (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-spectrometrically-sampled laser pyrolysis studies that show direct detection of NO and the nitroxyl radical (CH3)2NNO on a time scale too short to allow for the production of these substances in secondary bimolecular reactions; and (3) ab initio calculations that find a rearrangement pathway at slightly lower energy than that of simple bond scission.