Ionic Dynamics in molten salts and molten salt hydrates

在450-600K温度下，测量了熔融硫氰酸盐、KSCN和NaSCN中~lt；SCN~-&Gt~(2-)离子CN伸缩模的拉曼光谱。计算了振动和转动关联函数，并比较了&lt；Scn^-&Gt；离子在熔融态和水溶液中的动力学。用Kubo的随机线形理论分析了观测到的振动关联函数，其中均匀展宽和非均匀展宽同时处理。提取了对各向同性光谱的加宽贡献。均匀展宽随着温度的升高而增大，而熔融KSCN中的非均匀展宽保持不变，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~lt；Scn^-&gt；离子的转动相关函数表现为短时惯性转动(t&lt；&lt；！[&gt；0.15ps)，略慢于单个离子的自由转动。长时间指数衰减反映了离子重定向的最终扩散行为。测量和分析了&lt；(Nu)_1&gt；模~lt；NO(_3^-)&gt；在熔融硝酸盐及其二元混合物中的拉曼光谱。转动弛豫的机制以及配位数和浓度的涨落在振动退相中的作用将在不久的将来得到研究。

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.