Direct Dynamics Simulation of the Activation and Dissociation of 1,5-Dinitrobiuret (HDNB)

Abstract

Certain room-temperature ionic liquids exhibit hypergolic activity as liquid bipropellants. Understanding the chemical pathways and reaction mechanisms associated with hypergolic ignition is important for designing new fuels. It has been proposed ( J. Phys. Chem. A 2008, 112, 7816) that an important ignition step for the hypergolic ionic liquid bipropellant system of dicyanamide/nitric acid is the activation and dissociation of the 1,5-dinitrobiuret anion DNB-. For the work reported here, a quasiclassical direct dynamics simulation, at the DFT/M05-2X level of theory, was performed to model H+ + DNB- association and the ensuing unimolecular decomposition of HDNB. This association step is 324 kcal/mol exothermic, and the most probable collision event is for H+ to directly scatter off of DNB-, without sufficient energy transfer to DNB- for H+ to associate and form a highly vibrationally excited HDNB molecule. Approximately 1/3 of the trajectories do form HDNB, which decomposes by eight different reaction paths and whose unimolecular dynamics is highly nonstatistical. Some of these paths are the same as those found in a direct dynamics simulation of the high-temperature thermal decomposition of HDNB ( J. Phys. Chem. A 2011, 115, 8064), for a similar total energy.

Document Type

Article

DOI

https://doi.org/10.1021/jp5002622

Keywords

energy, molecular structure, molecular dynamics simulations, computational chemistry, molecules

Publication Date

2014

Journal Title

The Journal of Physical Chemistry A

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