The microscopic dynamics of several phases solid ethanol are studied under the same thermodynamic conditions by inelastic neutron scattering. It is found that vibrational density states orientational glass phase, where molecules arranged on an ordered lattice but with disordered orientations, very similar to structural both in position and orientation. Low-temperature specific heat measurements strongly support measurements. We therefore find positional disorder, even a stoichiometrically...

Superfluid ${}^{4}$He, a strongly correlated Bose-Einstein condensed many-body system, displays sharp phonon-roton quantized excitations. Here, the authors report complete determination of dispersion relation these excitations, using most advanced inelastic neutron scattering methods as well detailed dynamic theory calculations. From measured dispersion, obtain, analytically numerically, accurate tables thermodynamic properties. These highly precise results provide indispensable reference...

The origin of the well-defined collective excitations found in liquid para-H2 by recent experiments is investigated. persistence their relatively long lifetimes down to microscopic scales well accounted for calculations carried out means path-integral-centroid molecular dynamics. In contrast only overdamped are within classical limit. results provide fully quantitative evidence quantum effects on dynamics a simple liquid.

The existence of an orientationally disordered cubic phase solid ethanol is revealed by x-ray diffraction and Raman spectroscopic measurements. Such a phase, whose was postulated some time ago on the basis specific-heat measurements, produced quenching below 95 K plastic crystal formed upon melting subsequent annealing topologically (glassy) solid. relevance present findings for current discussions glassy dynamics analyzed in detail. \textcopyright{} 1996 American Physical Society.

The relationship between order at intermediate length scales and discernible features in the diffraction pattern of glassy liquid materials is demonstrated experimentally by means a direct comparison static structure factors material its liquid, stable crystal, rotator-phase orientational glass, amorphous phases. In addition, relevance orientationally disordered crystalline phases (i.e., either dynamic disorder crystal or quenched an glass), as stages topologically amorphous) solid,...

Abstract This work compares simulated and measured neutron time-of-flight spectra for a cold moderator with varying para-hydrogen concentrations (25%, 50%, 90% 99.9%) embedded in polyethylene thermal moderator. The primary neutrons are generated from the interaction of 45MeV protons tantalum target. simulations were performed using several Monte Carlo codes (MCNP, PHITS, McStas, VITESS, KDSource) together nuclear data ENDF/B-VII.1 JENDL $$-$$ <mml:math...

We present a full set of procedures to evaluate the experimental corrections needed derive physically meaningful quantities from measured neutron intensities in inelastic neutron-scattering experiments. Multiple-scattering are evaluated by means Monte Carlo code, which combination data and Synthetic Model is used account for neutron-molecule interactions. Multiphonon treated with an iterative scheme. To illustrate procedure densities vibrational states deuterated water ice near room...

Well-defined phonons with strong anomalous (upward) dispersion are observed by inelastic neutron scattering in liquid $para\ensuremath{-}{\mathrm{H}}_{2}$ at a temperature of 15.7 K. The damping, being very small for the low-$Q$ phonons, increases wave vector Q, and only broad features $Q\ensuremath{\gtrsim}1{\mathrm{\AA{}}\mathrm{}}^{\ensuremath{-}1}.$ This behavior is shown to deviate strongly from results molecular simulations fully classical analogue using realistic potential.

The vibrational spectrum of hydrogen atoms in magnesium hydride has been studied by means inelastic-neutron and Raman-scattering experiments between 12 295 K. After careful evaluation multiple scattering multiphonon contributions, we provide a frequency up to 180 meV the mean-square displacement atoms. inelastic light spectra ${\mathrm{MgH}}_{2}$ powders show three Raman allowed modes ${(A}_{1g},$ ${B}_{1g},$ ${E}_{g})$ some smaller features that can be related with second-order...

The dynamic structure factor of superfluid $^{4}\mathrm{He}$ has been investigated at very low temperatures by inelastic neutron scattering. measurements combine different incoming energies resulting in an unprecedentedly large range with excellent energy resolution, covering wave vectors $Q$ up to 5 ${\AA{}}^{\ensuremath{-}1}$ and $\ensuremath{\omega}$ 15 meV. A detailed description the dynamics is obtained from saturated vapor pressure solidification. single-excitation spectrum...

We investigate anomalies ascribed to quantum entanglement phenomena recently reported in deep inelastc neutron scattering (DINS) measurements by an independent technique on H(2)O/D(2)O mixtures. performed transmission experiments study several liquid mixtures at room temperature the epithermal energy range. obtain total cross sections of mixtures, which are agreement with expected results according tabulated values within a 0.3% relative error. observe no and stress limitations validity...

We investigated the neutron cross sections of hydrogen and deuterium by means deep inelastic neutron-scattering technique in H2O-D2O mixtures. The interest this work was to examine anomalous behavior section reported past similar experiments that raised a yet unsettled controversy. measurements were made at Bariloche pulsed source (Argentina) pure H2O D2O, with mixtures molar concentrations xD=0.3 0.4, room temperature, under same experimental conditions as former experiments. results are...

The dynamics of superfluid $^{4}\mathrm{He}$ at and above the Landau quasiparticle regime is investigated by high-precision inelastic neutron scattering measurements dynamic structure factor. A highly structured response observed familiar phonon-maxon-roton spectrum, characterized sharp thresholds for phonon-phonon, maxon-roton, roton-roton coupling processes. experimental factor compared to calculation same physical quantity a many-body theory including three-phonon processes...

We report on inelastic neutron scattering measurements of fully deuterated glassy glycerol at temperatures between 15 K to 180 K. Incident energies 40 and 100 meV momentum transfers up \ensuremath{\approxeq}12 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ were used. Analysis the static structure factor calculated as zeroth-frequency moment S(Q,\ensuremath{\omega}) enabled us derive valuable structural information intra- intermolecular correlations. Generalized frequency distributions are...

Measurements of the pressure dependence at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}80\mathrm{K}$ vibrational spectrum a polymorphic material in its amorphous (G), orientationally disordered crystal (ODC), and ordered (C) phases has permitted separation orientational site disorder effects on Gr\"uneisen parameters used here, pars pro toto, as measure anharmonicity. The greater anharmonicity found for G compared to ODC is consistent with their differences specific heat, while very...

We present a new formalism to obtain momentum distributions in condensed matter from Neutron Compton Profiles measured by the Deep Inelastic Scattering technique. The describes exactly as an integral variable $y$. As result we Volterra equation of first kind that relates experimentally magnitude with nuclei sample. integration kernel is related incident neutron spectrum, total cross section filter analyzer and detectors efficiency function. A comparison customarily employed approximation...