Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
J Chem Phys. 2012 Feb 7;136(5):054502. doi: 10.1063/1.3679875.
A neutron diffraction study was performed on the CD(4) : D(2)O structure H clathrate hydrate to refine its CD(4) fractional cage occupancies. Samples of ice VII and hexagonal (sH) methane hydrate were produced in a Paris-Edinburgh press and in situ neutron diffraction data collected. The data were analyzed with the Rietveld method and yielded average cage occupancies of 3.1 CD(4) molecules in the large 20-hedron (5(12)6(8)) cages of the hydrate unit cell. Each of the pentagonal dodecahedron (5(12)) and 12-hedron (4(3)5(6)6(3)) cages in the sH unit cell are occupied with on average 0.89 and 0.90 CD(4) molecules, respectively. This experiment avoided the co-formation of Ice VI and sH hydrate, this mixture is more difficult to analyze due to the proclivity of ice VI to form highly textured crystals, and overlapping Bragg peaks of the two phases. These results provide essential information for the refinement of intermolecular potential parameters for the water-methane hydrophobic interaction in clathrate hydrates and related dense structures.
一项关于 CD(4)：D(2)O 结构 H 包合物的中子衍射研究，旨在精确其 CD(4)的部分笼占有率。在巴黎-爱丁堡压机中生成冰 VII 和六方(sH)甲烷水合物的样品，并原位收集中子衍射数据。采用 Rietveld 方法对数据进行分析，得到水合物单元胞大二十面体(5(12)6(8))笼中平均有 3.1 个 CD(4)分子。sH 单元胞中每个正五边形十二面体(5(12))和十二面体(4(3)5(6)6(3))笼平均分别有 0.89 和 0.90 个 CD(4)分子。该实验避免了冰 VI 和 sH 水合物的共同形成，由于冰 VI 易于形成高度纹理化晶体和两种相的布拉格峰重叠，这种混合物更难分析。这些结果为水-甲烷疏水相互作用在包合物和相关致密结构中的分子间势能参数的精修提供了必要的信息。
