纤维素及磺酸类有机物的太赫兹光谱研究

发布时间：2018-03-18 18:11

本文选题：太赫兹光谱　切入点：密度泛函理论　出处：《电子科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：太赫兹光谱包含着丰富的物质结构信息,在材料鉴别、定量分析以及分子构象动力学等诸多基础与应用研究领域有着重要的应用。与无机材料相比,有机物在太赫兹波段的研究更为活跃。有机物的集体振动模式处于太赫兹波段,且种类繁多、易于设计成高效的太赫兹发射源和敏感的探测材料。然而,有机物的太赫兹振动模式尤为复杂,难于进行深入的分析和理解。这不仅不利于太赫兹光谱技术在表征和分析有机材料方面的应用,而且严重阻碍了探索性能优异的太赫兹新材料的步伐。为此,本文结合太赫兹光谱仪和基于密度泛函理论(DFT)的光谱计算,研究了纤维素及其同素异形体、氢键分子晶体牛磺酸以及有机磺酸盐DAST的太赫兹光谱及其响应原理,探究了固态DFT在准确预测部分结晶聚合物和氢键分子晶体太赫兹光谱的计算方法。本论文的主要成果包括:(1)采用低温溶解法制备了再生纤维素薄膜,对其物理形貌、结晶类型和化学成分进行了表征。首次指认并归属了再生纤维素(纤维素II)在0.1-21 THz波段的太赫兹指纹谱峰,提出一种利用太赫兹光谱来有效鉴别纤维素Iβ和纤维素II同素异晶体的新方法。指出再生纤维素的低频吸收峰源于其有序结晶部分的分子振动,据此提出一种适用于部分结晶聚合物光谱计算建模的简化处理方法。(2)以相对简单的氢键分子晶体牛磺酸为研究对象,指出固定晶格法和色散校正完全弛豫法在处理分子间相互作用方面的不同是导致两种方法预测的太赫兹光谱间差异的主要原因,揭示了色散校正在模拟氢键分子系统太赫兹光谱中的重要作用。首次指认并归属了固态牛磺酸在3-12 THz波段的太赫兹特征峰,还研究了牛磺酸太赫兹光谱的温度动力学特性,据此提出一种新型的三振子耦合模型合理地解释了实验上观测到的太赫兹特征峰随温度升高的反常蓝移现象。(3)采用逐步提高收敛精度的分步优化法,获得与实验一致的DAST基态结构,为进一步的模式分析提供了支持。首次对DAST太赫兹低频振动模式进行分析。结果表明1.12 THz处的振动是阴阳离子的光学声子模式,1.46 THz和1.54 THz两处的振动主要与磺酸盐阴离子有关,2.63 THz和3.16 THz处的振动源于阳离子的扭转振动和阴离子的转动。这些模式分析弥补了DAST太赫兹声子模式分析的空白,为今后设计合成具有二阶非线性的DAST衍生物提供了重要的参考和指导。
[Abstract]:The terahertz spectrum contains abundant material structure information and has important applications in the fields of material identification, quantitative analysis and molecular conformational kinetics. Organic compounds are more active in the terahertz band. The collective vibration modes of organic compounds are in the terahertz band, and they are easily designed as efficient terahertz emitters and sensitive detection materials. The terahertz vibration mode of organic compounds is particularly complex and difficult to be analyzed and understood in depth, which is not only unfavorable to the application of terahertz spectroscopy in the characterization and analysis of organic materials. Therefore, the study of cellulose and its isomorphism is based on the spectral calculation of terahertz spectrometer and density functional theory (DFT). Terahertz Spectra of hydrogen bonded Molecular Crystal taurine and Organic sulfonate DAST and its response principle, The calculation method for accurate prediction of terahertz spectra of some crystalline polymers and hydrogen-bonded molecular crystals by solid DFT has been investigated. The main achievements in this paper include: 1) the regenerated cellulose films were prepared by low temperature dissolution method and their physical morphology was investigated. The crystalline type and chemical constituents were characterized. The terahertz fingerprint peak of regenerated cellulose (Cellulose II) at the wavelength of 0.1-21 THz was identified and assigned for the first time. A new method for the identification of cellulose I 尾 and cellulose II isomers by using terahertz spectrum is proposed. It is pointed out that the low frequency absorption peak of regenerated cellulose originates from the molecular vibration of its ordered crystalline part. A simplified processing method for spectral modeling of partially crystallized polymers is proposed. The relatively simple hydrogen-bonded molecular crystal taurine is used as an object of study. It is pointed out that the difference between the fixed lattice method and the complete dispersion correction relaxation method in the treatment of intermolecular interaction is the main reason for the difference between the terahertz spectra predicted by the two methods. The important role of dispersion correction in the terahertz spectrum of the simulated hydrogen bond molecular system is revealed. The terahertz characteristic peaks of solid taurine in the 3-12 THz band are identified and assigned for the first time. The thermodynamics of the taurine terahertz spectrum is also studied. Based on this, a new coupling model of three oscillators is proposed to reasonably explain the abnormal blue shift phenomenon of terahertz characteristic peak observed in experiments with increasing temperature. The stepwise optimization method is used to improve the convergence accuracy step by step. The ground state structure of DAST is obtained, which is consistent with the experiment. It is the first time to analyze the low frequency vibration mode of DAST terahertz. The results show that the vibration at 1.12 THz is the optical phonon mode of anion and anion at 1.46 THz and 1.54 THz mainly with sulfonic acid. The vibration of salt anions at 2.63 THz and 3.16 THz originates from the torsional vibration of cations and the rotation of anions. These model analyses make up the gaps in the analysis of DAST terahertz phonon modes. It provides an important reference and guidance for the design and synthesis of DAST derivatives with second order nonlinearity.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O636.11;O623.84

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