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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopic and Computational Study of Acetic Acid and Its Cyclic Dimer in the Near-Infrared Region
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Spectroscopic and Computational Study of Acetic Acid and Its Cyclic Dimer in the Near-Infrared Region

机译：乙酸及其环状二聚体在近红外区的光谱和计算研究

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Anharmonic vibrational analysis of near-infrared (NIR) spectra of acetic acid was carried out by anharmonic quantum chemical calculation in a wide concentration range of its CCl4 solution. By predicting vibrational spectra of acetic acid for the first time over a wide NIR region, it was possible to elucidate the influence of the formation of acetic acid cyclic dimer on its NIR spectrum. Quantum chemical simulations were based on coupled cluster and density functional theory quantum methods. Additionally, Moller-Plesset perturbation theory was employed for the additional calculation of hydrogen bonding stabilization energies. An anharmonic vibrational analysis was performed with the use of generalized second-order vibrational perturbation theory (GVPT2). A hybrid approach was assumed, in which monomeric species was treated by CCSD(T)/aug-cc-pVDZ (harmonic approximation) and B3LYP/SNSD (anharmonic approximation) methods. For the cyclic dimer, B3LYP and B2PLYP single and double hybrid functionals, paired with an SNSD basis set, were employed. DFT calculations were augmented with additional empirical dispersion correction. It was found that quantum chemically calculated vibrational modes in the NIR region are in a good agreement with experimental data. The results of anharmonic vibrational analysis were supported by a harmonic shift analysis, for elucidating the very strong anharmonic coupling observed between stretching modes of hydrogen bonded bridge in the cyclic dimer. However, the calculated wavenumbers for combination modes of double hydrogen bonded bridge in the cyclic dimer, which are very sensitive to the formation of hydrogen bonding, were found to be underestimated by quantum chemical methods. Therefore, by band fitting, the wavenumbers and shape parameters for these bands were found, and the modeled spectra were adjusted accordingly. A high accuracy of simulated spectra was achieved, and a detailed analysis of the experimental NIR spectra of acetic acid was possible, with successful identification of numerous experimental bands, including those which originate from concentration effects. It was also found that the main spectral features observed in the NIR spectra of carboxylic acid upon the formation of hydrogen bond should be accounted for combination modes of the stretching and bending vibrations of double hydrogen-bonded bridge in the cyclic dimers of acetic acid.
机译：通过在宽浓度的CCl4溶液中进行非谐量子化学计算，对乙酸进行了近红外（NIR）光谱的非谐振动分析。通过首次预测乙酸在宽NIR区域的振动光谱，可以阐明乙酸环状二聚体的形成对其NIR光谱的影响。量子化学模拟基于耦合簇和密度泛函理论量子方法。此外，采用Moller-Plesset微扰理论对氢键稳定能进行了附加计算。使用广义二阶振动摄动理论（GVPT2）进行了非谐振动分析。假设采用一种混合方法，其中单体种类通过CCSD（T）/ aug-cc-pVDZ（谐波近似）和B3LYP / SNSD（非谐波近似）方法进行处理。对于环状二聚体，使用了B3LYP和B2PLYP单和双杂化功能以及SNSD基集。 DFT计算增加了附加的经验色散校正。发现在近红外区域内用量子化学方法计算的振动模态与实验数据吻合良好。非谐振动分析的结果得到谐波位移分析的支持，以阐明在环状二聚体中氢键桥的拉伸模式之间观察到的非常强的非谐耦合。但是，发现对环状二聚体中双氢键桥的结合模式的计算波数对氢键的形成非常敏感，但通过量子化学方法低估了该波数。因此，通过频带拟合，找到了这些频带的波数和形状参数，并相应地调整了建模光谱。可以实现高精度的模拟光谱，并且可以成功鉴定出许多实验谱带，包括源自浓度效应的谱带，从而可以对乙酸的实验NIR谱进行详细分析。还发现，在羧酸的近红外光谱中观察到的主要光谱特征是形成氢键的原因，这是乙酸循环二聚体中双氢键桥的拉伸和弯曲振动的组合方式。

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