1,721,084 research outputs found
Exploring ultra-fast proton dynamics in water under a static electric field
No full textWe present an experimental investigation of the single-particle dynamics of hydrogen
in liquid water and ice subject to static electric field using deep inelastic neutron scattering. The
nuclear mean kinetic energy, EK, of hydrogen in liquid water at room temperature does not
show sensible changes when an electric field of magnitude 105 V/m is turned on. On the contrary,
the value of EK in ice at 263 K and subject to the same electric field is found to be substantially
lower than the reference value for ice Ih at the similar temperature of 271 K and without electric
field. This is true both if the electric field is kept on or not while the sample cools from 300 K to
263 K. Concurrent diffraction measurements performed on ice subjected to an electric field show
no sizeable structural changes with respect to the expected powder-averaged ice-Ih diffraction
pattern
Microscopic collective dynamics in liquid neon-deuterium mixtures: Inelastic neutron scattering and quantum simulations
No full textIn this paper a combined neutron scattering and quantum simulation study of the collective dynamics in liquid Ne-D2 mixtures, at a temperature of T = 30 K and in the wave-vector transfer range 4 nm???1 < q < 51 nm???1, is presented. Two D2 concentrations are investigated, one close to 25% molar and the other close to 50% molar, together with pure Ne. The dynamic structure factor for the centers of mass of the two molecular species is extracted from the neutron scattering data and subsequently compared with that obtained from three different quantum simulation methods, such as ring polymer molecular dynamics and two slightly different versions of the Feynman-Kleinert approach. A general agreement is found, even though some discrepancies both among simulations, and between simulations and experimental data, can be observed. In order to clarify the physical meaning of the present spectroscopic results, an analysis of the longitudinal current spectral maxima is carried out showing the peculiarities of the D2 center-of-mass dynamics in these mixtures. A comparison with the centroid molecular dynamics results obtained for the D2 center-of-mass self-dynamics in the same liquid mixtures is finally proposed
Proton dynamics in supercritical water
Get PDFProton mean kinetic energy in supercritical water was determined using deep inelastic neutron scattering (DINS) technique to validate harmonic approximation and the hypothesis of decoupling among translational, rotational and vibrational degrees of freedom. Anisotropy of proton momentum distribution due to nonspherical molecular symmetry in water was also assessed. Proton mean kinetic energy was well described by a semi-classical harmonic model. The experimental results were found to be in good agreement with the theoretical predictions
Microscopic structure and collective modes in liquid hydrogen: a preliminary inelastic X-ray scattering study
No full textDouble difference method in deep inelastic neutron scattering on the VESUVIO spectrometer
No full text
Deep inelastic neutron scattering from orthorhombic ordered HCI: short-time proton dynamics and anomalous neutron cross-sections
No full textDeep inelastic neutron scattering measurements from orthorhombic ordered
HCl are presented and analyzed in order to clarify the problem of an
anomalous deficit in the neutron-proton cross section found in previous
experiments on various materials. A reliable model for the HCl
short-time single-particle dynamics, including atomic vibrational
anisotropies and deviations from the impulsive approximation, is set up.
The model HCl response function is transformed into simulated
time-of-flight spectra, taking carefully into account the effects of
instrumental resolution and the filter absorption profile used for
neutron energy analysis. Finally, the experimental values of the
anomalous reduction factor for the neutron-proton cross section are
extracted by comparing simulated and experimental data. Results show a
34\% reduction of the H cross section, varying with the scattering angle
in a range centered at 53 degrees. In addition, the same approximate
procedure used in earlier studies is also employed, providing results in
reasonable agreement with the more rigorous ones, and confirming the
substantial reliability of the past work on this subject
Measurement of momentum distribution of light atoms and molecules in condensed matter systems using inelastic neutron scattering
No full textStudies of single-particle momentum distributions in light atoms and
molecules are reviewed with specific emphasis on experimental
measurements using the deep inelastic neutron scattering technique at eV
energies. The technique has undergone a remarkable development since the
mid-1980s, when intense fluxes of epithermal neutrons were made
available from pulsed neutron sources. These types of measurements
provide a probe of the short-time dynamics of the recoiling atoms or
molecules as well as information on the local structure of the
materials. The paper introduces both the theoretical framework for the
interpretation of deep inelastic neutron scattering experiments and
thoroughly illustrates the physical principles underlying the impulse
approximation from light atoms and molecules. The most relevant
experimental studies performed on a variety of condensed matter systems
in the last 20 years are reviewed. The experimental technique is
critically presented in the context of a full list of published work. It
is shown how, in some cases, these measurements can be used to extract
directly the effective Born - Oppenheimer potential. A summary of the
progress made to date in instrument development is also provided.
Current data analysis and the interpretation of the results for a
variety of physical systems is chosen to illustrate the scope and power
of the method. The review ends with a brief consideration of likely
developments in the foreseeable future. Particular discussion is given
to the use of the VESUVIO spectrometer at ISIS
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