Abstract

Reorientation time is the basis of the calculation of microwave peak absorbing frequency (MPAF) of liquids. In the Stokes–Einstein–Debye theory, the reorientation time of polar molecules is considered mainly due to mechanical friction, and an obvious deviation exists between the predictions of this theory and the experimental observations. In this paper, with the theory of Onsager’s effective field, the phase relation between reaction field and rotating polar molecule is derived, and this reaction field hinders the rotation of molecules due to the hysteretic phase. Hence, the reorientation time is extended to the sum of mechanical reorientation time and dielectric reorientation time. With the relation of reorientation time of molecule and Debye relaxation time of dielectric, Debye relaxation time of dielectric is modified, and then an improved formula of MPAF is derived. The MPAFs of coumarin C522B, C307, C138 in alcohol solvents are calculated with this formula, and the changes in MPAFs of water, methanol and ethanol with temperature are also numerically studied. These calculated results are consistent with the experimental data.

Graphical abstract

中文翻译：

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含介电摩擦的极性液体微波吸收峰频率的计算

摘要

重新定向时间是计算液体的微波峰吸收频率（MPAF）的基础。在斯托克斯-爱因斯坦-德拜理论中，极性分子的重新定向时间主要是由于机械摩擦引起的，并且该理论的预测结果与实验观察结果之间存在明显的偏差。本文利用Onsager有效场理论推导了反应场与旋转极性分子之间的相位关系，该反应场由于滞后相而阻碍了分子的旋转。因此，重新定向时间延长到机械重新定向时间和介电重新定向时间之和。利用分子的重新定向时间与电介质的德拜弛豫时间的关系，可以修改电介质的德拜弛豫时间，然后推导了改进的MPAF公式。用该公式计算香豆素C522B，C307，C138在醇类溶剂中的MPAF，并数值研究了水，甲醇和乙醇的MPAF随温度的变化。这些计算结果与实验数据一致。

图形概要