High pressure Raman spectroscopy of single crystals of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).
High pressure Raman spectroscopy of single crystals of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).
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DOI：
10.1021/jp0681092
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发表时间：
2007-03
期刊：
影响因子：
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通讯作者：
Z. Dreger;Y. Gupta
中科院分区：
文献类型：
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作者：
Z. Dreger;Y. Gupta
为了深入了解RDX的高压多晶型，高能晶体，拉曼光谱的结果，获得了流体静力学（高达15 GPa）和非流体静力学（高达22 GPa）压缩。在4.0 +/- 0.3 GPa下发现了光谱中的几个明显变化，证实了先前在多晶样品中观察到的α-γ相变。详细的分析压力引起的内部和外部（晶格）模式的变化揭示了几个功能以上4 GPa：（i）分裂的A'和A“的内部模式，（ii）显着增加的压力依赖性的拉曼位移NO2模式，和（iii）没有明显的变化，外部模式的数量。有人提出，α-γ相变导致RDX分子之间的重排，这反过来又显着改变了分子间的相互作用所经历的N-O键。对称性相关分析表明，γ-多晶型物可能呈现三种正交结构之一：D2 h，C2 v或D2。根据现有的X射线数据，D2 h因子群优于其他结构，并提出γ相RDX具有与点群D2 h同构的空间群，其中8个分子占据C1对称位点，类似于α相。据信，因子群分裂可以解释所观察到的伽马相中模式数量的增加。空间映射的拉曼模式在非流体静力学压缩晶体高达22 GPa揭示了一个很大的差异，模式的位置，表明整个晶体的压力梯度。在非流体静力学压缩下，没有观察到明显的不可逆变化的拉曼光谱。
To gain insight into the high-pressure polymorphism of RDX, an energetic crystal, Raman spectroscopy results were obtained for hydrostatic (up to 15 GPa) and non-hydrostatic (up to 22 GPa) compressions. Several distinct changes in the spectra were found at 4.0 +/- 0.3 GPa, confirming the alpha-gamma phase transition previously observed in polycrystalline samples. Detailed analyses of pressure-induced changes in the internal and external (lattice) modes revealed several features above 4 GPa: (i) splitting of both the A' and A' ' internal modes, (ii) a significant increase in the pressure dependence of the Raman shift for NO2 modes, and (iii) no apparent change in the number of external modes. It is proposed that the alpha-gamma phase transition leads to a rearrangement between the RDX molecules, which in turn significantly changes the intermolecular interaction experienced by the N-O bonds. Symmetry correlation analyses indicate that the gamma-polymorph may assume one of the three orthorhombic structures: D2h, C2v, or D2. On the basis of the available X-ray data, the D2h factor group is favored over the other structures, and it is proposed that gamma-phase RDX has a space group isomorphous with a point group D2h with eight molecules occupying the C1 symmetry sites, similar to the alpha-phase. It is believed that the factor group splitting can account for the observed increase in the number of modes in the gamma-phase. Spatial mapping of Raman modes in a non-hydrostatically compressed crystal up to 22 GPa revealed a large difference in mode position indicating a pressure gradient across the crystal. No apparent irreversible changes in the Raman spectra were observed under non-hydrostatic compression.