Investigation On The Impact Sensitivities And Molecular Structures Of Polynitroaromatic Compounds

The pyrolysis of energetic materials is considered as an important step during the detonation of explosives. Especially the bond dissociation energy of the weakest bond plays a key role in the initial reaction. Studies on the bond dissociation energy can contribute to designing and synthesizing new explosives and propellants, which can promote the development of materials that combine improved performance with diminished vulnerability (sensitivity) to unintended external stimuli, such as impact and shock.It is being demonstrated with increasing frequency that density functional theory (DFT) can be an effective approach to compute reaction energetics. A key advantage over ab initio treatments of comparable accuracy is that density functional procedures can be applied to much larger systems. First of all, we test the effectiveness of four exchange/correlation combinations and five basis sets for computing the bond dissociation energies and dipole moments of a system including ozone, nitromethane, cyanogen, hexahydro-l,3,5-trinitro-l,3,5-triazine (RDX) and N-nitrodimethylamine. The B3P86 in conjunction with 6-31G** is found to give the best results for computing both bond dissociation energy and dipole moment.Secondly, using the best method (B3P86/6-31G**) determined by the above studies, we investigate the impact sensitivity of many species of polynitroaromatic molecules. The calculated results show that the impact sensitivity can be wellexplained by the C-NO2 bond dissociation energies. We find that the nitryl and amido have some effects on the impact sensitivity. When the number and position of the other substituted groups are the same, on the one hand, the impact sensitivity increases with the increasing of the number of nitryl. On the other hand, the impact sensitivity decreases with the increasing of the number of amido. In addition, it is found that the number of doorway modes in regions of 200cm"1 to 500cm"1 shows a correlation with the impact sensitivities obtained by drop hammers.Finally, the geometry of propyl nitrate is fully optimized using the B3LYP method and the standard 6-31G* basis set. The bond dissociation energies of propyl nitrate are calculated. Calculations show that the weakest bond is O-NO2 and the less weak bond is C-O. The pyrolysis mechanism of propyl nitrate is also discussed, and the products after the cleavage of O-NO2 as well as C-0 are predicted. In addition, the heats of formation are calculated by ab initio, semi-empirical, and density functional methods, and the result of PM3 is in agreement with the experimental data.