Direct experimental assessment of the strength of orientational correlations in polar liquids

Abstract

The strength of molecular orientational correlations in polar liquids is assessed by means of comparison of the diffuse scattering patterns of a liquid composed by molecules devoid of permanent electric dipole but having a weak quadrupole moment and those for a liquid composed by permanent molecular dipoles. The extent of orientational correlations within the liquid phases is in both cases assessed by comparison of the liquid radial distributions to those present in the rotator-phase (plastic) crystal phases of both compounds. For such disordered-crystal phases, information concerning orientational correlations is directly derived from the experimental scattering patterns by means of analysis of the diffuse scattering background present beneath the Bragg peaks. The results show that rather than long-ranged, orientational correlations in polar or polarizable liquids are confined within distances comprising the second coordination sphere.

The structure of liquid water beyond the first hydration shell

“…In agreement with previous works, it can be seen that molecules continue to fill the gaps of previous hydration shells in a more or less disordered way [32][33][34] . To make the meaning of g(θ pos , φ pos ) more intuitive, the same information is shown in this figure also as three-dimensional Spatial Distribution Maps 35 (SDM).…”

Comparison of short-range-order in liquid- and rotator-phase states of a simple molecular liquid: A reverse Monte Carlo and molecular dynamics analysis of neutron diffraction data

“…5, these are placed on the face of the molecule, which is the face-to-face-type configuration found in previous works. 5,7,10 For the next four neighbors, the orientation is ferromagnetic, and these are placed at the edges and corners of the molecule, giving rise to the previously determined pure interlocked 3 and Apollo 2 ͑i.e., two molecules with the C-Cl vectors parallel͒ configurations. The last four neighbors ͓Fig.…”

“…Details concerning the instrument settings and data correction procedures are given elsewhere. 10 The ODIC phase was prepared in situ following procedures already described. 10 The growth of a polycrystalline fcc phase was ascertained by the emergence of a set of crystalline Bragg peaks as described previously ͑see Ref.…”

“…That has been usually obtained by means of statistical analyses of the aforementioned ␣ angle between two randomly chosen C-Cl vectors of different molecules, but collapsing this information for all relative molecular positions, i.e., using P͑cos ␣͒. 7,10 Here, using the bivariate analysis, we can discriminate the relative orientation of two molecules ͑cos ␣͒ as a function of its position ͑cos ͒, i.e., P͑cos , cos ␣͒. As we have previously argued, we will distinguish between two possible main orientations only: ferromagnetic ͑cos ␣ =1͒ and antiferromagnetic ͑cos ␣ =−1͒.…”

“…The subject has received considerable attention over very many decades which have witnessed how the level of detail pertaining to the microscopic short-range order ͑SRO͒ of this molecular liquid has significantly increased, mainly due to the concurrence of computational techniques such as molecular dynamics ͑MD͒, 2,3 theoretical treatments based on the reference interaction site model ͑RISM͒, 4,5 as well as analysis of experimental diffraction patterns carried out by means of the reverse Monte Carlo ͑RMC͒ method. [6][7][8][9][10] The latter technique basically provides molecular configurations compatible with the measured structure factors S͑Q͒ or its representation in the real space, the total neutron weighted radial distribution function G͑r͒, by means of minimization of a cost function such as the chi-squared statistic between the observed data and that calculated for a given particle configuration, subject to a number of constraints imposed by the molecular structure as well as excluded volume considerations.…”