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Decomposition of Condensed Phase Energetic Materials: Interplay between Uni- and Bimolecular Mechanisms
journal contribution
posted on 2014-03-19, 00:00 authored by David Furman, Ronnie Kosloff, Faina Dubnikova, Sergey V. Zybin, William A. Goddard, Naomi Rom, Barak Hirshberg, Yehuda ZeiriActivation
energy for the decomposition of explosives is a crucial
parameter of performance. The dramatic suppression of activation energy
in condensed phase decomposition of nitroaromatic explosives has been
an unresolved issue for over a decade. We rationalize the reduction
in activation energy as a result of a mechanistic change from unimolecular
decomposition in the gas phase to a series of radical bimolecular
reactions in the condensed phase. This is in contrast to other classes
of explosives, such as nitramines and nitrate esters, whose decomposition
proceeds via unimolecular reactions both in the gas and in the condensed
phase. The thermal decomposition of a model nitroaromatic explosive,
2,4,6-trinitrotoluene (TNT), is presented as a prime example. Electronic
structure and reactive molecular dynamics (ReaxFF-lg) calculations enable to directly probe the condensed phase chemistry
under extreme conditions of temperature and pressure, identifying
the key bimolecular radical reactions responsible for the low activation
route. This study elucidates the origin of the difference between
the activation energies in the gas phase (∼62 kcal/mol) and
the condensed phase (∼35 kcal/mol) of TNT and identifies the
corresponding universal principle. On the basis of these findings,
the different reactivities of nitro-based organic explosives are rationalized
as an interplay between uni- and bimolecular processes.