Pusztai László, Pothoczki Szilvia, Kohara Shinji
Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, Budapest H-1525, Hungary.
J Chem Phys. 2008 Aug 14;129(6):064509. doi: 10.1063/1.2965820.
The total scattering structure factor of liquid tin tetraiodide (SnI(4)) has been interpreted by means of reverse Monte Carlo (RMC) modeling. From the sets of particle coordinates provided by RMC, which are consistent with experimental results within errors, partial radial distribution functions as well as correlation functions characterizing mutual orientations of molecules as a function of distance between molecular centers can be calculated. Interestingly and very much in contrast to liquids of symmetric XCl(4) molecules, the corner-to-face (or "Apollo")-type orientation of neighboring molecules has a significant (about 20%) occurrence in liquid SnI(4). Via comparison with a reference system, obtained by hard sphere Monte Carlo simulation, we demonstrate that intermolecular two-body correlations in liquid SnI(4) are determined largely by excluded volume (steric) effects; that is, intermolecular two-body interactions play only a minor role. On the other hand, as it is manifested in the large difference between the reference and "real" systems in terms of the orientational correlations, higher order interactions are indispensable. This feature can explain the extremely rich phase behavior of SnI(4) at high pressures.
液态四碘化锡（SnI₄）的总散射结构因子已通过反向蒙特卡罗（RMC）建模进行了解释。根据RMC提供的粒子坐标集（在误差范围内与实验结果一致），可以计算部分径向分布函数以及表征分子相互取向随分子中心间距变化的相关函数。有趣的是，与对称的XCl₄分子液体形成鲜明对比的是，相邻分子的角对面（或“阿波罗”）型取向在液态SnI₄中具有显著（约20%）的出现率。通过与硬球蒙特卡罗模拟得到的参考体系进行比较，我们证明液态SnI₄中的分子间两体相关性在很大程度上由排斥体积（空间位阻）效应决定；也就是说，分子间两体相互作用只起次要作用。另一方面，正如参考体系和“真实”体系在取向相关性方面存在巨大差异所表明的那样，高阶相互作用是不可或缺的。这一特征可以解释SnI₄在高压下极其丰富的相行为。
