Neutron diffraction study of structure of molten alkali hydroxides

1.用镍电池对熔融的LiOD、NaOD和KOD进行了中子散射测量。可以成功地从观测到的总强度中减去由该单元产生的大的散射强度。结构因子及其傅里叶变换表明，多原子离子可以具有有效的离子半径。通过分子动力学模拟结合中子散射测量，揭示了LiOH熔体的精细结构：(1)Li~+离子与OH~+离子配位主要在0原子一侧。最可能的位置是r_&lt；LiO&gt；=1.95A^ﾟ和Reta_&lt；Li-O-H&gt；=115ﾟ，这与LiOH分子在真空中的位置略有不同。(2)Li~(++)离子以一定的概率也在H原子一侧。这是固体中不存在的液体的特征之一。(3)就熔体的骨架结构而言，OH~+离子以四面体配位的方式围绕Li~+离子。另一方面，四个Li^+离子正好与OH^-离子的O原子配位，形成一个略微折叠的正方形平面。对LiOH、NaOH、KOH、RbOH和CsOH的偏振和去偏振喇曼散射也进行了测量。能带轮廓分析表明，振动弛豫率很大程度上取决于反阳离子，而转动弛豫率不是很大。在旋转自相关函数中，还发现了小t处的振荡性快速衰减和大t处的指数慢衰减。前者是由OH~+离子的释放引起的，后者似乎伴随着周围Li~(++)离子的结构重排。

1. Neutron scattering measurements have been performed for molten LiOD, NAOD, and KOD using a nickel metal cell. Large scattering intensities by the cell could be successfully subtracted from the observed total intensities. The structure factors and their Fourier transformations reveal that the polyatomic ion can possess an effective ionic radius.2. Fine structure of molten LiOH has been elucidated from molecular dynamics simulation combined with the neutron scattering measurement.(1) Li^+ ion coordinates OH^- ion mainly on the 0 atom side. The most probable location is that r_<LiO> = 1.95 A^^ﾟ and rheta_<Li-O-H> = 115ﾟ, which is somewhat different from that of LiOH molecule in vacuum.(2) The Li^+ ion coordinates in a certain probability also on the H atom side. This is one of the characteristics of liquids which cannot be found in the solid.(3) With regard to the framework structure of the melt, OH^- ion takes tetrahedral coordination around Li^+ ion. On the other hand, four Li^+ ions coordinate just to the O atom of the OH^- ion to form a slightly folded square plane.3. Polarized and depolarized Raman scattering measurements have also been accomplished for LiOH, NaOH, KOH, RbOH, and CsOH. Band contour analysis revealed that vibrational relaxation rate depends largely on the counter cations, while rotational relaxation rate does not so much. Also in the rotational autocor relation function, oscillatory rapid decay at small t and exponential slow one at large t are found. The former is caused by the liberation of the OH^- ion and the latter seems to be accompanied by structural rearrangement of the surrounding Li^+ ions.