F. P. Ricci

Microscopic structure of low temperature liquid ammonia: A neutron diffraction experiment

Neutron diffraction measurements on liquid ammonia at two temperature states on the liquid‐vapor coexistence curve are presented. Three isotropic mixtures of hydrogenated and deuterated ammonia have been studied and the three radial atom–atom distribution functions extracted at 213 K and 273 K. The comparison of the experimental results with the partial radial distribution functions for orientationally uncorrelated molecules, shows some evidence for hydrogen bonding in liquid ammonia but this is much less pronounced than that found in water under ambient conditions.

Self Diffusion in Liquid Water

The behavior of the self‐diffusion coefficient in water, along the coexistence curve for −31 °C⩽T⩽350 °C, is explained in terms of local fluctuations of free volume, energy per molecule, and ’’percentage of broken H bond’’ as derived from ir data. Our theoretical expression agrees with the experimental data, within their errors, in the overall range we considered. The transition to amorphous state is derived.

Orientational Correlations in Liquid and Supercritical CO2: Neutron Diffraction Experiments and Molecular Dynamics Simulations

Neutron diffraction data from sub- and supercritical CO2, collected over three different experimental runs, are analysed together, in order to investigate the evolution of the microscopic structure with the thermodynamic parameters. The relative orientations of neighbouring molecules are analysed also in terms of the angular radial correlation function, obtained by molecular dynamics simulation runs compatible with the total neutron weighted radial distribution function. Orientational correlations between neighbouring molecules are seen to persist across the whole thermodynamic range investigated. However, these are limited to the first neighbouring shell, and mainly ascribable to the quadrupolar interaction.

Orientational correlations and hydrogen bonding in liquid hydrogen chloride

Neutron diffraction data, obtained by employing the hydrogen isotope substitution technique, on orthobaric hydrogen chloride at two state points are presented. The site-site radial distribution functions are derived from these data and are compared with similar results obtained previously for hydrogen iodide and hydrogen bromide. Comparison of the measured hydrogen-hydrogen and chlorine-hydrogen radial distribution functions with those derived assuming uncorrelated orientations demonstrates the presence of strong orientational correlations between first neighboring HCl molecules at both states. An analysis of molecular configurations compatible with the experimental data as generated by a Monte Carlo simulation routine is used to discuss the extent of hydrogen bonding in liquid HCl.

Theoretical and experimental investigation of optical absorption anisotropy in β-Ga2O3

The question of optical bandgap anisotropy in the monoclinic semiconductor β-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk β-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift in the b onset is due to a suppression of the transition matrix elements of the three top valence bands at Γ point.

Orientational correlations in liquid hydrogen sulphide

Neutron diffraction data on liquid H2S, D2S and an equimolar mixture of the two are presented for two thermodynamic states along the liquid—vapour coexistence curve. Comparison of the site-site radial distribution functions obtained with those of a model fluid where orientational correlations are absent and with those of water demonstrates that, although hydrogen sulphide does not form hydrogen bonds, nevertheless weak orientational correlations between first neighbouring molecules are detectable in both thermodynamic states. An analysis of the molecular configurations compatible with the experimental data, as calculated by applying the empirical potential structural refinement, is presented also.

Role of hydrogen bond in self-diffusion process in liquid water

Abstract Comparing the self-diffusion coefficient between water and non associated liquids, we discuss the role of hydrogen bond in the diffusion process.

Search for size effects in the diffusion of Kr in CF4 at various densities

Experimental measurements of the diffusion coefficient of Kr in CF4atT = 243.15K in the density range 0 < ϱ ⪕ 1.75ϱc are reported. The experimental data are compared with those of self-diffusion of CF4 at the same temperature. The influence of the size effect on the diffusion process is shown for the first time in a real fluid, and it is compared with that of a hard sphere mixture.

Giant electroresistance and tunable magnetoelectricity in a multiferroic junction

First-principles density functional calculations show that the

On the Free Volume Theory and on the Macedo-Litovitz Hybrid Equation for Diffusion in Liquids

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