University of Sts. Cyril and Methodius, Faculty of Natural Sciences and Mathematics, Institute of Chemistry, Arhimedova 5, 1000 Skopje, Republic of Macedonia.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 May;75(5):1452-61. doi: 10.1016/j.saa.2010.01.016. Epub 2010 Feb 6.
The coupled-optical-phonon-mode theory of Barker and Hopfield of two mode interaction in isotropic crystals has been extended to monoclinic crystals. The analytical expressions for the calculation of the dielectric tensor elements in the ac crystal plane have been derived. It has been shown that the interaction dielectric model is a generalized expression of the dielectric tensor for monoclinic case when no interaction between modes is present. Also, the results of Barker and Hopfield are obtained from this more general theory, when an isotropic case is considered. In order to be able to investigate real crystals, meaning extending the interactions to a large number of pairs of modes, but at the same time to make the fitting procedure possible, a model dielectric function taking into account the interaction between modes with closest frequencies has been derived. The validity of the model obtained has been tested on a Tutton salt single crystal of K(2)Co(SO(4))(2).6H(2)O. The recorded spectra from the ac crystal plane were fitted in order to obtain best fit parameters. The comparison between the experimentally recorded spectra and the model reflectance function give good results and verify this model to be applicable.
已将 Barker 和 Hopfield 关于各向同性晶体中双模相互作用的耦合光学声子模式理论扩展到单斜晶体。已经推导出用于计算交流晶体平面介电张量元素的解析表达式。结果表明，当不存在模式之间相互作用时，相互作用介电模型是单斜晶情况下介电张量的广义表达式。此外，当考虑各向同性情况时，还可以从这个更一般的理论中得到 Barker 和 Hopfield 的结果。为了能够研究真实晶体，即扩展相互作用到大量的模式对，但同时又能使拟合过程成为可能，已推导出考虑最接近频率的模式之间相互作用的模型介电函数。已经在 K(2)Co(SO(4))(2).6H(2)O 的 Tutton 盐单晶上测试了所获得的模型的有效性。为了获得最佳拟合参数，对交流晶体平面的记录光谱进行了拟合。实验记录的光谱与模型反射函数之间的比较给出了良好的结果，验证了该模型的适用性。
