Modeling Defect-Induced Phenomena

Abstract

Elucidation of dissociation mechanisms, energy localization, and transfer phenomena in the course of explosive decomposition of energetic materials (EMs) are central for understanding, controlling, and enhancing the performance of these materials as fuels, propellants, and explosives. Quality of energetic materials is often judged using two main parameters: sensitivity to detonation and its performance. Low sensitivity is desired to make the material relatively stable to external stimuli, i.e., controllable and able of triggering rapid dissociation only when needed and not accidentally. Performance, on the other hand, is to be high to provide larger heat of the explosive reaction. These parameters do not necessarily correlate with each other and depend on many variables such as molecular and crystalline structures, history of samples, the particle size, crystal hardness and orientation, external stimuli, aging, storage conditions, and others. Mechanisms governing performance are fairly well understood whereas mechanisms of sensitivity are poorly known and need to be much more extensively studied. It is widely accepted though that the thermal decomposition reactions of the materials play a significant role in their sensitivity to mechanical stimuli and their explosive properties [1]. The decomposition of energetic materials can be initiated with a mechanical impact, thermal heating, a shock wave, or a spark. Such events in solids generate molecules in highly excited vibronic and/or electronic states. Clearly, the decomposition of solid explosives under shock, spark, laser, or plasma ignition must include contributions from both ground and excited electronic states. Excitation in the UV can markedly reduce the power requirements for detonation of some secondary explosives. Therefore, establishing the initial steps of high explosive (HE) decomposition is an important goal to pursue. Decomposition triggered by excited electronic states seems appealing because electronic excitation of the system to an unstable potential energy surface can result in rapid dissociation of a molecule and consequent chain reaction.