An excitonic mechanism of detonation initiation in explosives

Abstract

Line-imaging velocimetry for observing spatially heterogeneous mechanical and chemical responses in plastic bonded explosives during impact Rev. Sci. Instrum. 84, 083903 (2013); 10.1063/1.4817307 Band-gap tuning at the strong quantum confinement regime in magnetic semiconductor EuS thin films Appl. Phys. Lett. 100, 211910 (2012); 10.1063/1.4720167Compression-induced effect on the electronic structure of cyclotrimethylene trinitramine containing an edge dislocation A novel mechanism for detonation initiation in solid explosives is proposed. This is based on electronic excitations induced by an impact wave propagating through the crystal. We illustrate the model by using the RDX ͑C 3 H 6 N 6 O 6 ) crystal as an example. In our model, a key role belongs to lattice defects, in particular edge dislocations, which promote dramatic changes in the electronic structure, primarily a reduction of the optical gap due to the splitting off of local electronic states from both valence and conduction bands. The pressure inside the impact wavefront further reduces the band gap, making it close to zero. This promotes highest occupied molecular orbital-lowest unoccupied molecular orbital HOMO-LUMO transitions resulting in N-NO 2 bond breaking and the creation of favorable conditions for the initiation of a chain reaction. Experimental facts supporting the suggested mechanism are discussed.

First-principles anisotropic constitutive relationships in β-cyclotetramethylene tetranitramine (β-HMX)

“…may influence the sensitivity of an EM, 38,39 but in the case of ␤-HMX we have not observed a substantial reduction in the band gap toward zero.…”

A model for mechanochemical transformations: Applications to molecular hardness, instabilities, and shock initiation of reaction

“…The calculational experiments by Kunz and co-workers 6 have shown lattice deformations can significantly decrease the HOMO-LUMO gap for molecules and further demonstrate that any excess strain, such as that associated with a shock wave or defects, can further reduce the gap, as originally suggested by Gilman. 7 For the specific case of RDX, the calculations clearly indicate that the gap closure leads a single N-NO 2 bond to break.…”

“…But when the electronic energy decreases (IϪAϩ⌫Q)→0, (Q)→1/2, and an energy level, which has 2t bandwidth and population 1 2 , is formed. Thus, we have obtained the condition for the critical deformation, ͗Q͘ cd ϭϪ(IϪA)/⌫, which causes HOMO-LUMO gap closure-the state which Gilman 6 has called local metallization and which is a special case of DIMED. Figure 4 gives a visual interpretation of the critical deformation energy.…”

“…Further elaboration on the excitonic mechanism of detonation initiation for RDX ͑hexahydro-1,3,5-trinitro-1,3,5-triazine͒ crystal is found in a recent informative study by Kunz and co-workers. 6 The model, based on numerical results, suggests that the pressure inside the impact wave front reduces the band gap between valence and conducting bands and promotes the HOMO-LUMO transition within a molecule. 6 Gilman's strain-induced HOMO-LUMO gap closing, 7 the Kunz group calculations, 6 and our previous model 8 for solid state reactions have stimulated us to investigate in detail an electronic instability mechanism for molecular decomposition and its relation to the mechanoelectronic effect.…”

“…This has been reviewed by Faust,4 and recently addressed for secondary explosives. 5,6 The essence of the idea is that a shock wave can generate molecules in highly excited electronic states, a mechanoelectronic effect. Thus the initiating reaction due to shock is taken to be an electronic mechanism.…”