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首页> 外文期刊>Spectrochimica acta, Part A. Molecular and biomolecular spectroscopy >Study of polarized IR spectra of the hydrogen bond system in crystals of styrylacetic acid
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Study of polarized IR spectra of the hydrogen bond system in crystals of styrylacetic acid

机译：苯乙烯乙酸晶体中氢键体系的偏振红外光谱研究

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We have investigated the polarized IR spectra of the hydrogen bond system in crystals of trans-styrylacetic acid C6H5-CH=CH-CH2-COOH, and also in crystals of the following three deuterium isotopomers of the compound: C6H5-CH=CH-CH2-COOD, C6H5-Cl-4=CH-CD2-COOH and C6H5-CH=CH-CD2-COOD. The spectra were measured at room temperature and at 77 K by a transmission method. The spectral studies were preceded by determination of the X-ray crystal structure. Theoretical analysis of the results concerned linear dichroic effects, the H/D isotopic and temperature effects, observed in the solid-state IR spectra of the hydrogen and of the deuterium bond, at the frequency ranges of the VO-H and the v(O-D) bands, respectively. Basic spectral properties of the crystals can be interpreted satisfactorily in terms of the "strong-coupling" theory, when based on a hydrogen bond dimer model. This model sufficiently explained not only a two-branch structure of the VO-H and the VO-D bands, and temperature-induced evolution of the crystalline spectra, but also the linear dichroic effects observed in the band frequency ranges. A vibronic mechanism was analyzed, responsible for promotion of the symmetry-forbidden transition in the IR for the totally symmetric proton stretching vibrations in centrosymmetric hydrogen bond dimers. It was found to be of minor importance, when compared with analogous spectral properties of arylcarboxylic acid, or of cinnamic acid crystals. These effects were ascribed to a substantial weakening of electronic couplings between the hydrogen bonds of the associated carboxyl groups and the styryl radicals, associated with the separation of these groups in styrylacetic acid molecules by methylene groups in the molecules. (c) 2005 Elsevier B.V. All fights reserved.
机译：我们已经研究了反式-苯乙烯酸C6H5-CH = CH-CH2-COOH晶体以及以下三种氘代同位素的氢键体系的极化红外光谱：C6H5-CH = CH-CH2 -COOD，C 6 H 5 -Cl-4 ＝ CH-CD 2 -COOH和C 6 H 5 -CH ＝ CH-CD 2 -COOD。通过透射法在室温和77K下测量光谱。在进行光谱研究之前，先确定X射线晶体的结构。对结果的理论分析涉及在VO-H和v（OD）频率范围内的氢和氘键的固态IR光谱中观察到的线性二向色效应，H / D同位素和温度效应）乐队。当基于氢键二聚体模型时，可以根据“强耦合”理论令人满意地解释晶体的基本光谱性质。该模型不仅充分说明了VO-H和VO-D波段的两分支结构，以及温度引起的晶体光谱演化，还充分说明了在波段频率范围内观察到的线性二向色效应。分析了一个振动机制，该机制负责促进中心对称氢键二聚体中完全对称的质子拉伸振动在红外中的对称禁止跃迁。与芳基羧酸或肉桂酸晶体的类似光谱性质相比时，发现其重要性不大。这些作用归因于相关的羧基的氢键和苯乙烯基之间的电子偶联的显着减弱，这与通过分子中的亚甲基将苯乙烯基乙酸分子中的这些基团分离有关。 （c）2005 Elsevier B.V.版权所有。

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