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共晶是一种分子层次调控材料物化性质的高效方法,然而目前共晶复杂体系结构与宏观性质间关系一直难以得到深入理解.本文依据太赫兹光谱可激发晶体内弱作用的优势,以CL-20/MTNP共晶为对象开展了太赫兹振动光谱研究.首先,测量CL-20、MTNP和共晶CL-20/MTNP的太赫兹吸收光谱.其次,分析了基于密度泛函理论的振动计算方法,获得了三种物质太赫兹频段振动特性,对吸收光谱进行了振动匹配.最后,采用振动分解方法将晶体分子的整体振动分解为分子间和分子内振动.在此基础上,分析了共晶前后振动变化规律.结果表明:共晶后新形成的弱相互作用由CL-20分子主导,同时MTNP分子主要通过三个硝基与CL-20分子交互作用.本文的研究结论为共晶热性质的提升提供了微观解析.Cocrystals represent an effective approach to manipulate the physicochemical properties of materials at the molecular level. However, understanding the relationship between their complex crystal structures and macroscopic properties has been a challenge. In this paper, based on the advantage of terahertz (THz) spectroscopy in characterizing non-covalent interactions within crystals, we conduct the THz vibrational spectroscopy study on the CL-20/MTNP cocrystal. Firstly, the THz spectra of CL-20, MTNP, and the CL-20/MTNP cocrystal were measured at room temperature. Both absorption positions and intensities of the cocrystal differ from those of its original components, confirming the unique advantage of terahertz spectroscopy in cocrystal identification. Secondly, the THz vibrational features of the three materials are calculated based on density functional theory (DFT). Then, the experimental absorptions were matched with the calculated vibrations. Furthermore, a vibrational decomposition method was employed to dissect the molecular vibrations into intermolecular and intramolecular vibrations. The vibrational variations of the cocrystal compared to its original components were analyzed. The results reveal that in the cocrystal, the intermolecular vibrational modes of both CL-20 and MTNP molecules undergo alterations compared to their raw materials. This suggests that the non-covalent interactions within the cocrystal modify the original intermolecular interactions between these molecules. Consequently, this enhancement promotes heat transfer between MTNP and CL-20 molecules, thereby improving the thermal stability of the cocrystal. In conclusion, the findings of this study demonstrate that THz vibrational spectroscopy technology is instrumental in establishing a relationship between the molecular structure of cocrystals and their macroscopic properties. This research contributes to advancing our understanding of cocrystal systems and opens up new avenues for material design and optimization.
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Keywords:
- Terahertz spectroscopy /
- Density functional theory /
- Vibrational decomposition /
- CL-20 cocrystal
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