双环-HMX结构和性质的理论研究

Theoretical Study on the Structures and Properties of Bicyclo-HMX

在DFT-B3LYP/6-311G水平上,计算研究了高能化合物四硝基四氮杂双环辛烷(双环-HMX)α和β两种异构体的结构和性质.比较分子对称性、分子内氢键和环张力等几何参数以及分子总能量和前线轨道能级等电子结构参数,发现α比β稳定.分子中N—N键较长,N—N键集居数较小,预示该键为热解和起爆的引发键.基于简谐振动分析求得IR谱频率和强度.运用统计热力学方法求得200～1000K温度的热力学性质.以非限制性半经验PM3方法探讨其热解机理,求得各反应通道的过渡态和活化能,发现热解始于侧链N—NO2键的均裂.还从理论上预测了该化合物的密度、爆速和爆压,有助于寻求高能量密度材料(HEDM).

The compound tetranitrotetraazabicyclooctane (bicyclo-HMX) has been calculated by using the density functional theory method at the B3LYP/6-311G* level. There are two optimized molecular geometries: alpha (1H,5H-cis) and beta (1H,5H-trans) conformations. Based on the comparison of molecular symmetry, intramolecular hydrogen bonds, ring strain, total energies and frontier orbital energies, it was found that a conformation is more stable than P. The bond lengths of N-N are longer and Mulliken population of N-N is smaller than the other bonds in bicyclo-HMX, which means that the N-N may be the initial bond in pyrolysis and explosion. Normal-mode analyses were used to characterize the stable point and to determine the harmonic vibrational frequencies. Thermodynamic properties at 200 similar to 1000 K were provided using statistical thermodynamic method. Pyrolysis mechanism was investigated using unrestricted Hatree-Fock model of semi-empirical PM3 method, getting each transition state and activation energy, and finding that the rupture of side N-NO2 bond is preferential. And the density, detonation velocity and pressure of bicyclo-HMX were predicted, which will set a foundation to look for high energy density materials.