Study Of The Terahertz Spectrum Of FOX-7

1,1-diamino-2,2-dintroethylene(FOX-7,also called DADE),a novel explosive with high energy and low sensibility.Up to now,only a few research groups at home and abroad have done some preliminary research on FOX-7,and they mainly focus on the preparation and characterization,which involved structural properties,sensibility,energy,thermal decompositation,etc.While In terms of molecular structure,the intramolecular and intermolecular modes which arising from macromolecular skeleton vibration,crystal lattice vibration,van der Waals force,and crystal transformation caused by the structural changes can provide rich characteristics spectrum information in the terahertz range.Therefore,it has a certain significance to carry out the experimental study of the terahertz spectrum of FOX-7 under normal temperature,variable temperatures and mixed state with other explosives in order to better understand its crystal structure,the vibration of the characteristic s groups and the process crystal transformation.Combining experimental and theoretical method was used in this article,the main contents of this article including:(1)Using terahertz time-domain spectroscopy(THz-TDS)to carry out the transmission terahertz spectra experiments under different conditions which forenamed,the absorption spectra were detected online.The characteristic absorption peaks of ? and ? form of single compound FOX-7 within the range of 0.2~2.5 THz were ascertained through the analysis of the absorption spectra of mixed explosives.There was a characteristic absorption peak for ? form FOX-7 which locked at 2.12 THz,two characteristic absorption peaks locked at 1.12,2.13 THz for ? form FOX-7,and the new absorption peak at 1.12 THz was caused by structural changes of FOX-7 in the heating process.(2)The single molecule and molecular crystal of ? form FOX-7 were optimized by density functional theory(DFT),and the vibrational frequency were calculated.The theoretical model-molecular crystal,which was more closed to the state of experimental solid explosive,was ascertained by comparing the differences between the calculation results and the experimental data,and the experimental absorption spectrum was analyzed based on the calculation results of the crystal structure.The vibrational modes of the characteristic peaks of two kinds of crystalline in the experimental absorption spectra were analyzed and identified.The changes of structure and energy of FOX-7 in the heating process were analyzed based on the simulation results,the crystal volume will gradually became larger,while the crystal density gradually decreases before the temperature raised to 111?.When the temperature was 111?,the process of phase transformation from ? form to ? form would occurred.The article also showed that the ? form of FOX-7 is more stable than ? form by evaluating the maintaining energy of two crystal shape.