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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Study of the single-crystal X-ray diffuse scattering in paracetamol polymorphs
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Study of the single-crystal X-ray diffuse scattering in paracetamol polymorphs

机译：对乙酰氨基酚多晶型物的单晶X射线扩散散射研究

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Single-crystal diffuse X-ray scattering from paracetamol polymorphs is successfully calculated with Monte Carlo (MC) models that are used to simulate the crystals. In order to obtain the correct model appropriate force constants are required that describe the interatomic potentials used in the MC algorithm. Coefficients for an empirical Buckingham-type formula are used to determine these force constants. These coefficients are subsequently refined using the least-squares method and are found to converge on similar values for both polymorphic forms. An investigation of the correlation space generated from each model provides what would be expected given that strong displacive correlations exist between the molecules comprising the densely hydrogen-bonded layers. More disordered motions between these layers are present in the model for form (II) as opposed to form (I). An investigation into the peculiarities of librational disorder was also conducted, however, correlation values turn out to be so small that any structural information concerning librational correlation is inconclusive. The purpose of this experiment was to identify if the diffuse scattering features could provide further insight into understanding the physical reasoning behind the metastability of form (II). The form (II) → (I) phase transition is also not currently well understood and usually phase transitional information can be obtained from pronounced diffuse scattering features. Since the diffuse scattering is modelled adequately using harmonic potentials it is our conjecture that the 'diffuse' is essentially thermal in origin and does not afford any extra information about the form (II) → (I) phase transition.
机译：对乙酰氨基酚多晶型物的单晶扩散X射线散射已使用Monte Carlo（MC）模型成功计算出来，该模型用于模拟晶体。为了获得正确的模型，需要适当的力常数来描述MC算法中使用的原子间电势。经验白金汉式公式的系数用于确定这些力常数。随后，使用最小二乘法对这些系数进行精炼，发现这两种多态形式收敛于相似的值。对每个模型生成的相关空间的研究提供了预期的结果，因为在构成密集氢键层的分子之间存在强置换相关性。与形式（I）相反，形式（II）的模型中存在这些层之间的更多无序运动。还对自由主义障碍的特殊性进行了研究，但是，相关性值是如此之小，以至于与自由性相关性有关的任何结构性信息都没有定论。本实验的目的是确定弥散散射特征是否可以提供进一步的见解，以了解形式（II）的亚稳态背后的物理原因。形式（II）→（I）的相变目前还不是很了解，通常可以从明显的漫散射特征中获得相变信息。由于可以使用谐波电位对散射进行充分建模，因此我们推测“散射”的起源本质上是热的，并且不提供任何有关形式（II）→（I）相变的信息。

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