A Pathway to the Athermal Impact Initiation of Energetic Azides

Energetic materials (explosives, propellants and pyrotechnics) are used in a broad range of public and private sector applications. The design of novel, safe materials is therefore of critical importance. Until now, no physical mechanism has been described to rationalize the impact sensitivity properties of energetic materials. Investigation therefore has required lengthy synthesis and experimental testing. Based on knowledge of the effects of mechanical impact, an ab initio model is developed to rationalize and describe the impact sensitivity of a series of crystalline energetic azide materials. It is found that electronic excitation of the azido anion is sufficient for initiation of these materials. The athermal excitation can be achieved through consideration of non-adiabatic, vibronic processes. Across the series of azides studied here, the electronic structure of the azido anion is found to remain largely constant. By considering only the relative rates of vibrational energy transfer within the crystalline materials, it is found that a direct correlation exists between the relative impact sensitivity and the rate of energy up-conversion. Thus, the present contribution demonstrates a fully ab initio method to describe the athermal initiation of ideal, crystalline energetic materials, and predict their relative sensitivity. Without the need for any experimental input beyond a crystal structure, this method therefore offers a means to selectively design novel materials for targeted application.