STFC, ISIS facility, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK.
J Phys Condens Matter. 2010 Oct 13;22(40):404212. doi: 10.1088/0953-8984/22/40/404212. Epub 2010 Sep 22.
The microscopic structure of neat formic and acetic acid have been measured by neutron diffraction with H/D substitution on SANDALS at the ISIS neutron spallation source. These data, together with complementary x-ray data, have been modeled via the empirical potential structure refinement (EPSR) method, which integrates information obtained from the diffraction data in a Monte Carlo simulation in order to provide a three-dimensional model of the system under study compatible with the measured structure factors. Two models have been generated for each acid, in order to test their consistency, with positive results. The final structure obtained is that of two liquids that are very similar to each other, with high connectivity although rather disordered. They present a hierarchy of probability for hydrogen bond formation, where weaker bonds involving the carbonyl hydrogen for formic acid or the methyl hydrogen for acetic acid are more abundant than the stronger bonds involving the hydroxyl hydrogen. Cooperative effects are found to be fundamental for the description of aggregation of formic and acetic acid, but the structure in the liquid presents a greater variety of bonds than in the solid state.
已通过 SANDALS 在 ISIS 散裂中子源上用 H/D 取代对甲酸和乙酸的纯态进行中子衍射，测量了其微观结构。这些数据与补充的 X 射线数据一起，通过经验势结构精修（EPSR）方法进行了建模，该方法将从衍射数据中获得的信息集成到蒙特卡罗模拟中，以提供与所测量结构因子相匹配的研究体系的三维模型。针对每种酸都生成了两个模型，以检验其一致性，结果为阳性。最终得到的结构是两种非常相似的液体，尽管有些无序，但连接性很高。它们呈现出氢键形成的概率层次结构，其中涉及甲酸的羰基氢或乙酸的甲基氢的较弱键比涉及羟基氢的较强键更为丰富。发现协同效应对于描述甲酸和乙酸的聚集是至关重要的，但液体中的结构比固态中呈现出更多种类的键。
