Six-nitro-Di (HNS) Photolysis Studies

HNS (2,2’,4,4’,6,6’-hexanitrostillbene, C14H6N6O12) is a heat-resistant explosive, which is widely used in booster charge, mild detonating fuse, and heat-stable explosive due to its excellent thermal stability, high detonation sensitivity and low critical diameter and so on. HNS has also been considered as a typical photosensitive explosive for the photodecomposition appears to be easily occurred. However, past studies of HNS are mostly focused on the preparation, particle size controlling, thermal decomposition behaviour, ignition and combustion performance and propagation capability and so on. No related investigation about the photodecomposition of HNS has been reported in detail. Determination of the photodecomposition mechanism, photolytic degradations kinetics, and the degradation products and identification of intermediates are very important for a better understanding of explosive lifetime prediction. Additionally, understanding the photodecomposition mechanisms and dynamics will allow for better control and improvement of the performance of energetic materials for combustion and explosion. Therefore, in this paper the photodecomposition of HNS is investigated both experimentally and theoretically. The main contents are listed as follows:The absorption wavelength of HNS is obtained in the range of full wavelength in different solvents. The solvate effect on the absorption wavelength is investigated. The selectivity of HNS molecule on the light source is determined.An experimental analysis has been subjected to study the UV-induced photodecomposition of HNS. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) measurements are used to study the structure changes of HNS before and after UV-irradiation. The possible decomposition channel upon UV irradiation is discussed. Results show that C-NO2broken and nitro-nitrite isomerization with subsequent release of NO would be both existed in the photodecomposition of HNS. The differential scanning calorimetry (DSC) experiments have shown that there is no influence on the thermal stability of HNS powders as the effect of UV irradiation.The effects of laser irradiation on HNS, especially at the irradiation of different laser wavelengths (including263nm wavelength,527nm wavelength and1053nm wavelength) and different laser power density are studied by X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and asynchronous two-dimensional correlation FT-IR spectra and so on. The possible decomposition channels are discussed. Results showe photodecomposition mechanism of HNS is wavelength-dependent. In the case of263nm and527nm irradiated, the nitro-nitriteisomerization and the fragmentation of trans-C=C bond are the main decomposition steps, while in the case of1053nm, only the fragmentation of trans-C=C bond is observed.A novel approach to study the photo-thermal decomposition of HNS (2,2’,4,4’,6,6’-hexanitrostillbene) at532nm induced by a10-nanosecond (ns) laser was described. In this method, an in-situ X-ray photoelectron spectroscopy (XPS)-laser-quadrupole mass spectrum on-line equipment was designed elaborately. The ultra high vacuum (10-9mbar) and high cleanliness of XPS analyzer chamber was fully exploited. The HNS film was directly irradiated by532-nm laser during XPS and MS spectra collection, thus enabling the accurate analysis of the photo-thermal decomposition. XPS and MS results showed that the nitro-nitrite isomerization with subsequent release of NO is the primary reaction in the laser-induced decomposition of HNS.Laser photolysis of HNS in acetonitrile solution is investigated with the excitation wavelength of355nm under different saturated conditions. The transient absorption spectra of HNS are investigated using nanosecond laser photolysis technique. The half-life of formation and decay rate of the transient absorption are calculated. In order to know how many kinds of transient species arised when HNS is excited by355nm laser, fluorescene and phosphorescen spectra are measured by time-resolved fluorescene and phosphorescen spectrometer. Results show that there are three kinds of transient species.In quantum chemistry calculation, all molecular structures are optimized by using Density Functional Theory (DFT) at B3LYP/6-311G (d, p) level. The charge distribution, the interaction of orbits, the electronic structure, the photodecomposition mechanism and the thermal performance are estimated. The calculation results could explain the experimental resultd preferably.