33 research outputs found
Investigation of the structural disorder in ice Ih using neutron diffraction and Reverse Monte Carlo Modelling
Structure determination of liquid carbon tetrabromide via a combination of x-ray and neutron diffraction data and reverse Monte Carlo modeling
In order to reveal the atomic level structure of liquid carbon tetrabromide,
a new synchrotron x-ray diffraction measurement, over a wide momentum transfer
(Q-)range, has been performed. These x-ray data have been interpreted together
with a neutron diffraction dataset, measured earlier, using the reverse Monte
Carlo method. The structure is analysed on the basis of partial radial
distribution functions and distance dependent orientational correlation
functions. Orientational correlations behave similarly to other carbon
tetrahalides. Moreover, the information content of the new x-ray diffraction
data set, and in particular, of the varying Q-range, is also discussed.
Only very small differences have been found between results of calculations
that apply one single experimental structure factor and the ones that use both
x-ray and neutron diffraction data: the latter showed slightly more ordered
carbon-carbon radial distribution function, which resulted in seemingly more
ordered orientational correlations between pairs of molecules. Neither the
extended Q-range, nor the application of local invariance constraints yielded
significant new information. For providing a simple reference system, a hard
sphere model has also been created that can describe most of the partial radial
distribution functions and orientational correlations of the real system at a
semi-quantitative level.Comment: Accepted for publication in Journal of Molecular Liquids, (notice
and) citation to the published article inserte
The structure of PX3 (X=Cl, Br, I) molecular liquids from X-ray diffraction, Molecular Dynamics simulations and Reverse Monte Carlo modeling
Synchrotron X-ray diffraction measurements have been conducted on liquid
phosphorus trichloride, tribromide and triiodide. Molecular Dynamics
simulations for these molecular liquids were performed with a dual purpose: (1)
to establish whether existing intermolecular potential functions can provide a
picture that is consistent with diffraction data; (2) to generate reliable
starting configurations for subsequent Reverse Monte Carlo modelling.
Structural models (i.e., sets of coordinates of thousands of atoms) that were
fully consistent with experimental diffraction information, within errors, have
been prepared by means of the Reverse Monte Carlo method. Comparison with
reference systems, generated by hard sphere-like Monte Carlo simulations, was
also carried out to demonstrate the extent to which simple space filling
effects determine the structure of the liquids (and thus, also estimating the
information content of measured data). Total scattering structure factors,
partial radial distribution functions and orientational correlations as a
function of distances between the molecular centres have been calculated from
the models. In general, more or less antiparallel arrangements of the primary
molecular axes that are found to be the most favourable orientation of two
neighbouring molecules. In liquid PBr3 electrostatic interactions seem to play
a more important role in determining intermolecular correlations than in the
other two liquids; molecular arrangements in both PCl3 and PI3 are largely
driven by steric effects.Comment: 25 pages, 6 figure
Neutron diffraction of hydrogenous materials: measuring incoherent and coherent intensities separately from liquid water - a 40-year-old puzzle solved
(short version) Accurate determination of the coherent static structure
factor of disordered materials containing proton nuclei is prohibitively
difficult by neutron diffraction, due to the large incoherent cross section of
H. This notorious problem has set severe obstacles to the structure
determination of hydrogenous materials up to now, via introducing large
uncertainties into neutron diffraction data processing. Here we present the
first accurate separate measurements, using polarized neutron diffraction, of
the coherent and incoherent contributions to the total static structure factor
of 5 mixtures of light and heavy water, over an unprecedentedly wide momentum
transfer range. The structure factors of HO and DO mixtures derived in
this work may signify the beginning of a new era in the structure determination
of hydrogenous materials, using neutron diffraction.Comment: 8 page
Folyadék és amorf szerkezetű anyagok vizsgálata diffrakcióval és számítógépes modellezéssel = Investigations of liquid and amorphous structures by diffraction and computer modelling methods
Eredeti pályázatunknak megfelelően elsősorban folyadékok szerkezetét vizsgáltuk (elsősorban röntgen)diffrakciós módszerrel és az azt követő Reverse Monte Carlo (RMC) modellezéssel. Az elnyert támogatás a világ legnagyobb teljesítményű szinktrotronforrásánál, a SPring-8-nél (Hyogo, Japán) végzett (nagyenergiás) röntgendiffrakciós kísérleteket tett lehetővé. Meghatároztuk nagynyomású, szobahőmérsékletű folyékony (szuperkritikus állapotban lévő) oxigén és nitrogén lokális szerkezetét; úgy találtuk, hogy a szomszédos molekulák párhuzamos beállása mellett az 'X'-alakú konformáció is gyakori. Azonosítottuk az ón-tetrajodid folyadékfázisát mint azt az anyagot, amelyben a legnagyobb arányban fordulnak elő a szabályos tetraéder alakú molekulák 'csúcs-lap' (azaz 'Apollo') típusú illeszkedése. Az XCl4 szabályos tetraéder alakú molekulákból álló folyadékokban (X: C, Si, Ge, Sn) a vártnál (valamint az eddigiekben javasolthoz képest) lényegesebb hosszabb, néhány nanométerre kiterjedő orientációs rendezettséget találtunk. | According to our original project plan, we've investigated primarily liquid structures, using (primarily X-ray) diffraction methods and subsequent Reverse Monte Carlo modeling. The support awarded made it possible to carry out (high energy) X-ray diffraction experiments at the world's most powerful synchrotron source, SPring-8 (Hyogo, Japan). We have determined the local structure of high-pressure, room temperature liquid (supercritical fluid) oxygen and nitrogen; it was found that apart from the parallel configuration, neighboring molecules frequently choose 'X'-shaped mutual orientations. We have identified liquid tin tetraiodoide as the material which contains the highest ratio of 'corner-to-face' (or so-called 'Apollo') type conformations of molecules with perfect tetrahedral shape. In liquids of XCl4 (perfect tetrahedral) molecules (X: C, Si, Ge, Sn) a rather long (much longer than expected and than had been suggested before), nanometer range orientational ordering of molecules
Structural, Rheological and Dynamic Aspects of Hydrogen-Bonding Molecular Liquids: Aqueous Solutions of Hydrotropic tert-Butyl Alcohol
Hypothesis: The structural details, viscosity trends and dynamic phenomena in t-butanol/water solutions are closely related on the molecular scales across the entire composition range. Utilizing the experimental small- and wide-angle x-ray scattering (SWAXS) method, molecular dynamics (MD) simulations and the ‘complemented-system approach’ method developed in our group it is possible to comprehensively describe the structure-viscosity-dynamics relationship in such structurally versatile hydrogen-bonded molecular liquids, as well as in similar, self-assembling systems with pronounced molecular and supramolecular structures at the intra-, inter-, and supra-molecular scales. Experiments: The SWAXS and x-ray diffraction experiments and MD simulations were performed for aqueous t-butanol solutions at 25 °C. Literature viscosity and self-diffusion data were also used. Findings: The interpretive power of the proposed scheme was demonstrated by the extensive and diverse results obtained for aqueous t-butanol solutions across the whole concentration range. Four composition ranges with qualitatively different structures and viscosity trends were revealed. The experimental and calculated zero-shear viscosities and molecular self-diffusion coefficients were successfully related to the corresponding structural details. The hydrogen bonds
2 that were, along with hydrophobic effects, recognized as the most important driving force for the formation of t-butanol aggregates, show intriguing lifetime trends and thermodynamic properties of their formation