Diffraction by Molecular Liquids

Blum, L.; Narten, A. H.

doi:10.1002/9780470142530.ch4

Cited by 67 publications

(8 citation statements)

References 57 publications

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“…in the case of naphthalene. Similar principles were discussed earlier by Narten and co-workers for applications in molecular liquids . For flexible, macromolecular fluids, for instance, it is no longer possible to uniquely separate the total scattering structure function (or PDF) into intra- and inter-molecular contributions.…”

Section: Real-space Structure Characteristicsmentioning

confidence: 59%

“…Differences in the bonding properties along the chain versus between neighboring chain structures can affect the relative sharpness or broadness of the associated peaks, similar to the broadening observed for intermolecular peaks from small molecules. Furthermore, the effects of chain rigidity or persistence length and the overall small contribution from the pairs along a single chain to the total PDF at higher distances can lead to a significant loss of distinct atom-pair peak details at longer distances along the chain. , Thus, the MRO and LRO signals in the PDF, if present, often reflect lower frequency density modulations that result from the packing directions perpendicular to the 1D chains. This is demonstrated simply using the density fluctuations of stacked cylinders.…”

Section: Real-space Structure Characteristicsmentioning

confidence: 99%

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Structural Analysis of Molecular Materials Using the Pair Distribution Function

2021

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This is a review of atomic pair distribution function (PDF) analysis as applied to the study of molecular materials. The PDF method is a powerful approach to study short-and intermediate-range order in materials on the nanoscale. It may be obtained from total scattering measurements using X-rays, neutrons, or electrons, and it provides structural details when defects, disorder, or structural ambiguities obscure their elucidation directly in reciprocal space. While its uses in the study of inorganic crystals, glasses, and nanomaterials have been recently highlighted, significant progress has also been made in its application to molecular materials such as carbons, pharmaceuticals, polymers, liquids, coordination compounds, composites, and more. Here, an overview of applications toward a wide variety of molecular compounds (organic and inorganic) and systems with molecular components is presented. We then present pedagogical descriptions and tips for further implementation. Successful utilization of the method requires an interdisciplinary consolidation of material preparation, high quality scattering experimentation, data processing, model formulation, and attentive scrutiny of the results. It is hoped that this article will provide a useful reference to practitioners for PDF applications in a wide realm of molecular sciences, and help new practitioners to get started with this technique.

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Section: Real-space Structure Characteristicsmentioning

confidence: 59%

Section: Real-space Structure Characteristicsmentioning

confidence: 99%

Structural Analysis of Molecular Materials Using the Pair Distribution Function

2021

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“…Az elmúlt sok évtized folyamán számos ilyen közelítés született (ld.pl. [Powles 1972, Blum 1976, Rickayzen 1979, Granada 1987, Dawidowski 1994, Palomino 2007])a pontos alak azonban a legutóbbi időkig ] nem volt ismeretes. E probléma miatt dolgozatomban kizárólag a nehézvíz neutrondiffrakciós mérési adatát tekintem [Soper 1997], amelyet az első mérések óta ] megbízhatónak fogad el a kutatóközösség.…”

Section: I32 Röntgendiffrakcióunclassified

Számítógépes modellezési vizsgálatok a tiszta víz szerkezetvizsgálatával kapcsolatban: a kölcsönhatási potenciálok és a mért diffrakciós adatok közötti konzisztencia kérdése

Steinczinger¹

2016

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“…Figure 1 shows the incoherent intensities, which are directly proportional to the spin incoherent cross sections, up 21 Å −1 , along with numerical fits in the form of Gaussian functions plus a constant. Note that this functional form, that has not been suggested explicitly by any of the corresponding studies of the coherent background [11][12][13][14][15][16][17], operates with only 3 adjustable parameters (see 'Methods'). The residuals are also shown in Figure 1; it is obvious that the differences between fits and measured curves are exclusively of statistical nature.…”

mentioning

confidence: 99%

“…It has been clear for many decades that reliable neutron total structure factors of water samples with high light water content (ideally, of pure 1 H 2 O) would be decisive concerning H-bonding in water. For this reason, numerous suggestions over the past 40 years have been made for the treatment of the huge 'incoherent background' (for an informative figure, see, e.g., [1]), none of which has proven to be routinely applicable (for the various approaches, see [11][12][13][14][15][16][17]). Real improvement could be expected only from an accurate experimental determination of the incoherent contributions from 1 H. Spin-incoherence, the major cause of the troubles, can in principle be tackled by separating the coherent and incoherent parts of the measured diffraction signal; this can be achieved by using polarised neutrons (see, e.g., Ref.…”

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confidence: 99%

Neutron diffraction of hydrogenous materials: Measuring incoherent and coherent intensities separately

et al. 2015

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Accurate determination of the coherent static structure factor of any disordered material containing substantial amounts of proton nuclei has proven to be prohibitively difficult by neutron diffraction, due to the extremely large incoherent cross section of 1 H. This notorious problem has continued to set severe obstacles to the reliable determination of liquid structures of hydrogenous materials up to this day, by introducing large uncertainties whenever a sample with a 1 H content larger then about 20 % had to be measured by neutron diffraction. Huge theoretical efforts over the past 40 years that had been aimed at estimating the 'incoherent background' of such data have not resulted in any practical solution to the problem. Here we present the first accurate separate measurements, by polarised neutron diffraction, of the coherent and incoherent contributions to the total static structure factor of mixtures of light and heavy water, over an unprecedentedly wide momentum transfer range, and over the entire composition range, i.e. for light water contents between 0 and 100 %. We show that the measured incoherent background can be approximated by a Gaussian function. The separated coherent intensities exhibit signs of small inelastic contributions. Out of several possible approaches, we have chosen to subtract a cubic background using the Reverse Monte Carlo algorithm, which has the advantage of requiring an actual physical model (thousands of realistic water molecules at the correct density) behind the corrected data. Finally, coherent static structure factors for 5 different compositions of liquid H2O and D2O mixtures are presented for which the large incoherent background could actually be measured and separated, instead of being approximated as it has been done every time so far. These unprecedented experimental results provide a strong hope that determining the structure of hydrogenous materials, including, e.g., protein solutions, may become feasible in the near future.

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Diffraction by Molecular Liquids

Cited by 67 publications

References 57 publications

Structural Analysis of Molecular Materials Using the Pair Distribution Function

Structural Analysis of Molecular Materials Using the Pair Distribution Function

Számítógépes modellezési vizsgálatok a tiszta víz szerkezetvizsgálatával kapcsolatban: a kölcsönhatási potenciálok és a mért diffrakciós adatok közötti konzisztencia kérdése

Neutron diffraction of hydrogenous materials: Measuring incoherent and coherent intensities separately

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