Ivanovski Vladimir, Mayerhöfer Thomas G, Stare Jernej, Gunde Marta Klanjšek, Grdadolnik Jože
Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University in Skopje, Arhimedova 5, 1000 Skopje, Macedonia.
Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, D-07745 Jena, Germany; Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University, Helmholtzweg 4, Jena D-07743, Germany.
Spectrochim Acta A Mol Biomol Spectrosc. 2019 Jul 5;218:1-8. doi: 10.1016/j.saa.2019.03.094. Epub 2019 Mar 28.
In contrast to the extensive molecular and crystal structure investigations on oxalic acid dihydrate (CHO·2HO, α-POX) and its deuterated analogues (α-DOX), stands the absence of a complete vibrational spectra analysis. Such analysis is desirable in view of the proton dynamics in α-POX crystals. In this communication we report the room temperature polarized IR reflectance spectra of a single crystal of α-POX recorded from the ac crystal plane, and from the plane containing the b-crystallographic axis, with polarization along the axis. Dispersion analysis of the reflectance spectra of both B and A symmetry type modes, using model dielectric and reflectance function valid for the monoclinic case, have been performed and the results are discussed. Some aspects of the obtained fit results for some of the spectral regions and the peculiar change of the reflectance function with polarization angle are also discussed in this work. A correlation between the crystal structure and measured spectra, together with the results of the performed dispersion analysis, gave answers to some of the problems concerned with the orientation of the transition dipole moments of the IR active modes. The assignment of modes is assisted by DFT calculations. Another aspect covered in this work is the model reflectance functions using different averaging theories that have been applied in obtaining the reflectance spectrum of a polycrystalline sample. The results of the comparison between these spectra and the recorded reflectance spectra from a polycrystalline sample were further discussed.
与对二水合草酸（CHO·2HO，α-POX）及其氘代类似物（α-DOX）进行的广泛分子和晶体结构研究形成对比的是，目前缺乏完整的振动光谱分析。鉴于α-POX晶体中的质子动力学，这种分析是很有必要的。在本通讯中，我们报告了从ac晶面以及包含b晶轴的平面记录的α-POX单晶在室温下的偏振红外反射光谱，偏振方向沿该轴。使用对单斜晶系情况有效的模型介电常数和反射函数，对B和A对称型模式的反射光谱进行了色散分析，并对结果进行了讨论。本文还讨论了某些光谱区域的拟合结果以及反射函数随偏振角的特殊变化的一些方面。晶体结构与测量光谱之间的相关性，以及所进行的色散分析结果，为一些与红外活性模式的跃迁偶极矩取向有关的问题提供了答案。模式的归属由密度泛函理论计算辅助。本文涵盖的另一个方面是使用不同平均理论的模型反射函数，这些理论已应用于获得多晶样品的反射光谱。进一步讨论了这些光谱与多晶样品记录的反射光谱之间的比较结果。
