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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Terahertz Spectroscopy and Solid-State Density Functional Theory Calculations of Cyanobenzaldehyde Isomers
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Terahertz Spectroscopy and Solid-State Density Functional Theory Calculations of Cyanobenzaldehyde Isomers

机译：氰基苯甲醛异构体的太赫兹光谱和固态密度泛函理论计算

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摘要

Spectral signatures in the terahertz (THz) frequency region are mainly due to bulk vibrations of the molecules. These resonances are highly sensitive to the relative position of atoms in a molecule as well as the crystal packing arrangement. To understand the variation of THz resonances, THz spectra (2-10 THz) of three structural isomers: 2-, 3-, and 4-cyanobenzaldehyde have been studied. THz spectra obtained from Fourier transform infrared (FTIR) spectrometry of these isomers show that the resonances are distinctly different especially below 5 THz. For understanding the intermolecular interactions due to hydrogen bonds, four molecule cluster simulations of each of the isomers have been carried out using the B3LYP density functional with the 6-31G(d,p) basis set in Gaussian09 software and the compliance constants are obtained. However, to understand the exact reason behind the observed resonances, simulation of each isomer considering the full crystal structure is essential. The crystal structure of each isomer has been determined using X-ray diffraction (XRD) analysis for carrying out crystal structure simulations. Density functional theory (DFT) simulations using CRYSTAL14 software, utilizing the hybrid density functional B3LYP, have been carried out to understand the vibrational modes. The bond lengths and bond angles from the optimized structures are compared with the XRD results in terms of root-mean-square-deviation (RMSD) values. Very low RMSD values confirm the overall accuracy of the results. The simulations are able to predict most of the spectral features exhibited by the isomers. The results show that low frequency modes (<3 THz) are mediated through hydrogen bonds and are dominated by intermolecular vibrations.
机译：太赫兹（THz）频率范围内的光谱特征主要是由于分子的整体振动。这些共振对分子中原子的相对位置以及晶体堆积排列高度敏感。为了了解THz共振的变化，已研究了三种结构异构体（2-，3-和4-氰基苯甲醛）的THz光谱（2-10 THz）。从这些异构体的傅里叶变换红外（FTIR）光谱获得的太赫兹光谱表明，共振明显不同，尤其是在5 THz以下。为了理解由于氢键引起的分子间相互作用，使用在Gaussian09软件中设置的具有3-31G（d，p）基的B3LYP密度泛函对每个异构体进行了四个分子簇模拟，并获得了顺应性常数。但是，要了解所观察到的共振背后的确切原因，考虑全晶体结构的每种异构体的模拟是必不可少的。已使用X射线衍射（XRD）分析来确定每种异构体的晶体结构，以进行晶体结构模拟。已经进行了使用CRYSTAL14软件的密度泛函理论（DFT）模拟，并利用混合密度泛函B3LYP来理解振动模式。根据均方根偏差（RMSD）值将优化结构的键长和键角与XRD结果进行比较。 RMSD值非常低，可以确认结果的整体准确性。模拟能够预测异构体表现出的大多数光谱特征。结果表明，低频模式（<3 THz）是通过氢键介导的，并受分子间振动的支配。

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