Ionic Dynamics in molten salts and molten salt hydrates

在温度450 ~ 600k的熔融硫氰酸盐、KSCN和NaSCN中，测量了<SCN^- b>离子的CN拉伸模式的拉曼光谱。计算了振动和旋转相关函数，并比较了<SCN^->离子在熔融态和水溶液中的动力学。用Kubo的随机线形理论对观测到的振动相关函数进行了分析，其中同时处理了均匀和非均匀展宽。提取了各向同性光谱的两种展宽贡献。均匀展宽随温度升高而增加，而非均匀展宽在熔融KSCN中保持不变，这被认为是导致各向同性拉曼带宽温度展宽的原因。熔体中<SCN^->离子的旋转相关函数表现出短时间惯性旋转(t <<！[> 0.15ps]，这比单个离子的自由旋转要慢一点。长时间的指数衰减反映了离子重取向的最终扩散行为。在熔体和水溶液中，旋转弛豫速率随温度的升高而增大。本文测量和分析了熔融硝酸盐及其二元混合物中<NO(_3^-)>离子<(nu)_1>模式的拉曼光谱。旋转松弛的机制以及配位数和浓度的波动在振动减相中的作用将在不久的将来得到进一步的研究。

The Raman spectra of the CN stretching mode of <SCN^-> ions were measured in molten thiocyanates, KSCN and NaSCN, at temperatures 450-600K. The vibrational and rotational correlation functions were calculated, and the dynamics of <SCN^-> ions in the molten state are compared with those in aqueous solutions. The observed vibrational correlation functions are analysed by the stochastic line shape theory of Kubo, in which homogeneous and inhomogeneous broadening are treated simultaneously. Both broadening contributions to the isotropic spectra are extracted. The homogeneous broadening increases with increasing temperature, while inhomogeneous broadening remains constant in molten KSCN, which is considered to lead to the temperature broadening of the isotropic Raman bandwidth. Rotational correlation functions of <SCN^-> ions in melts show the behavior of short time inertial rotation (t <<![> 0.15ps), which is a little slower than the free rotation of a single ion. The long time exponential decay reflects the ultimate diffusional behavior of the ionic reorientation. The rotational relaxation rate is found to increase with temperature in both melts and aqueous solutions.The Raman spectra of the <(nu)_1> mode of <NO(_3^-)> ions in molten nitrates and their binary mixtures are now measured and analysed. The mechanisms of rotational relaxation and the roles of fluctuations of coordination number and concentration in the vibrational dephasing will be studied in the near future.