Energy transfer rates and impact sensitivities of crystalline explosives

Abstract

The energy transfer rates between phonons and vibrons in the “doorway region” could be the rate-determining step for impact-induced detonation of molecular crystalline explosives. To investigate the relationship between impact sensitivities and energy transfer, the overall rate of energy transfer in the doorway region is estimated on the basis of a simple theory in which the rate is proportional to a product of the number of states and the rate of population relaxation. We estimated frequencies of normal mode vibrations of PETN, β-HMX, RDX, Tetryl, TNT, FOX-7, m-DNB, ANTA, PN, NQ, NTO, and DMN by means of density functional theory calculations at the B3LYP/6-31G(d) level of theory. Normal mode vibrations of TATB were evaluated by using empirical intra-molecular potentials. The number of doorway modes in the regions of 200 to 700 cm −1 was evaluated by the direct counting method. It is found that the number of doorway modes shows a strong correlation with impact sensitivities obtained by drop hammer tests. This can be explained by the theory, if we assume that the rate of population relaxation is almost the same for all of the explosives investigated in the present work. This assumption is consistent with recent experimental measurements of energy transfer rates of explosives at low temperatures.