Thermal Decomposition of 1,5-Dinitrobiuret (DNB): Direct Dynamics Trajectory Simulations and Statistical Modeling
Abstract
A large set of quasi-classical, direct dynamics trajectory simulations were performed for decomposition of 1, 5-dinitrobiuret (DNB) over a temperature range from 4000 to 6000 K, aimed at providing insight into DNB decomposition mechanisms. The trajectories revealed various decomposition paths, and reproduced the products (including HNCO, N2O, NO2, NO, and water) observed in DNB pyrolysis experiments. Using trajectory results as a guide, structures of intermediate complexes and transition states that might be important for decomposition were determined using density function theory calculations. Rice-Ramsperger-Kassel-Marcus (RRKM) theory was then utilized to examine behaviors of the energized reactant and intermediates and to determine unimolecular rates for crossing the various transition states. According to RRKM predictions, the dominant initial decomposition path of energized DNB corresponds to elimination of HNNO2H via a concerted mechanism where the molecular decomposition is accompanied with intra-molecular H-atom transfer from the central nitrogen to the terminal nitro oxygen. Other important paths correspond to elimination of NO2 and H2NNO(pi). NO(2) elimination is a simple N-N bond scission process. Formation and elimination of nitramide is however dynamically complicated, requiring twisting a -NHNO2 group out of the molecular plane, followed by an intramolecular reaction to form nitramide before its elimination. These two paths become significant at temperature above 1500 K, accounting for greater than 17% of DNB decomposition at 2000 K. This work demonstrates that quasi-classical trajectory simulations, in conjunction with electronic structure and RRKM calculations, are able to extract mechanisms, kinetics, dynamics and product branching ratios for the decomposition of complex energetic molecules, and predict how they vary with decomposition temperature.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 03, 2011
- Accession Number
- ADA547366
Entities
People
- Ghanshyam L Vaghjiani
- Jianbo Liu
- Steven D Chambreau
Organizations
- Air Force Research Laboratory