Theoretical Predictions Of The Initial Decomposition Steps Of Dimethylnitramine
JOURNAL OF CHEMICAL PHYSICS(2005)
摘要
The structures and energies of the reactants, products, and transition states of the initial steps in the gas-phase decomposition of dimethylnitramine (DMNA) have been determined by quantum chemical calculations at the B3LYP density-functional theory, MP2, and G2 levels. The pathways considered are NO2 elimination, HONO elimination, and nitro-nitrite rearrangement. The NO2 elimination is predicted to be the main channel of the gas-phase decomposition of DMNA in accord with experiment. The values of the Arrhenius parameters, log A=16.6 +/- 0.5 and E-a=40.0 +/- 0.6 kcal/mol, for the N-NO2 bond-fission reaction were obtained using a canonical variational theory with B3LYP energies and frequencies. The HONO-elimination channel has the next lowest activation energy of 44.7 +/- 0.5 kcal/mol (log A=13.6 +/- 0.5) and is characterized by a five-member transition-state configuration in which a hydrogen atom from one of the methyl groups is transferred to an oxygen atom of NO2. Tunneling contributions to the rate of this reaction have been estimated. The nitro-nitrite rearrangement reaction occurs via a transition state in which both oxygen atoms of NO2 are loosely bound to the central nitrogen atom, for which Rice-Ramsperger-Kassel-Marcus theory predicts log A=14.4 +/- 0.6 and E-a=54.1 +/- 0.8 kcal/mol. (c) 2005 American Institute of Physics.
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关键词
transition state theory,nitrogen,rate constant,activation energy,quantum effect,reaction kinetics,perturbation theory,product distribution,transition state,cross section,density function theory
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