Structure and disorder in ice VII on the approach to hydrogen-bond symmetrization
Structure and disorder in ice VII on the approach to hydrogen-bond symmetrization
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DOI：
10.1103/physrevb.99.184112
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发表时间：
2019-05-23
影响因子：
3.7
通讯作者：
Tulk, C.
中科院分区：
文献类型：
--
作者：
Guthrie, M.;Boehler, R.;Tulk, C.
我们已经收集了足够质量的中子衍射数据的结构改进从氘冰VII超过60 GPa。在这些压力下，我们正在接近分子离解的开始，水分子应该被显著扭曲。我们拟合我们的数据与传统的结构模型冰VII和最近提出的“间隙”模型。我们发现这些在统计上是不可区分的，因此，在这项工作中采用了传统的模型。我们的改进产生的第一个直接的实验测定的分子结构，在这种压力制度。它们显示了共价键的明显伸长，其速率随压力迅速增加，表明我们已经进入了接近冰X的独特区域。此外，我们已经直接测量的压力依赖性的分离的两个等价的氘核网站沿着氢键，这提供了一个上限的氢键中心压力。
We have collected neutron-diffraction data of sufficient quality for structural refinement from deuterated ice VII to over 60 GPa. At these pressures, we are approaching the onset of molecular dissociation where the water molecule should be significantly distorted. We fitted our data with both the conventional structural model for ice VII and a recently proposed "interstitial" model. We found these to be statistically indistinguishable and, therefore, adopted the conventional model in this work. Our refinements yield the first direct experimental determination of the molecular structure in this pressure regime. They show a clear elongation of the covalent bond, the rate of which rapidly increases with pressure, indicating we have entered a distinct regime on the approach to ice X. In addition, we have directly measured the pressure dependence of the separation of the two equivalent deuteron sites along the hydrogen bonds, which provides an upper bound on the hydrogen-bond centering pressure.