A combined INS and DINS study of proton quantum dynamics of ice and water across the triple point and in the supercritical phase

Senesi

2016

J. Phys. Chem. Lett.

This study presents the first direct and quantitative measurement of the nuclear momentum distribution anisotropy and the quantum kinetic energy tensor in stable and metastable (supercooled) water near its triple point, using deep inelastic neutron scattering (DINS). From the experimental spectra, accurate line shapes of the hydrogen momentum distributions are derived using an anisotropic Gaussian and a model-independent framework. The experimental results, benchmarked with those obtained for the solid phase, provide the state of the art directional values of the hydrogen mean kinetic energy in metastable water. The determinations of the direction kinetic energies in the supercooled phase, provide accurate and quantitative measurements of these dynamical observables in metastable and stable phases, that is, key insight in the physical mechanisms of the hydrogen quantum state in both disordered and polycrystalline systems. The remarkable findings of this study establish novel insight into further expand the capacity and accuracy of DINS investigations of the nuclear quantum effects in water and represent reference experimental values for theoretical investigations.A large number of experimental and theoretical dynamical studies of liquid water near the triple point are available in literature; 1−9 nevertheless, a full and accurate characterization of hydrogen dynamics is still lacking. The latter is of vital importance for clarifying thermodynamic properties and the key to expand our understanding of some of the mysterious characteristics of water, supercooled water (SW), and glassy water, the latter being its viscous counterparts, known as amorphous ice. 10 Nuclear quantum effects (NQEs) play an important role in water, ice, and hydrogen-bonded systems and directly influence their microscopic structure and dynamical properties. In most of these cases, the hydrogen atoms are localized in potential wells with pronounced zero point motion. The equilibrium hydrogen dynamics is reflected in the quantum momentum distribution, n(p), a quantity which provides complementary information to what is garnered from diffraction techniques. Because of NQEs, n(p) markedly differs from the classical Maxwell−Boltzmann distribution, being determined almost entirely by the quantum mechanics of the vibrational ground state properties. 11−17 This makes n(p) a highly sensitive probe of the local environment, fingerprinting any changes occurring both in the structure of the hydrogen-bonded network as well as in the local symmetry. Thus, n(p) together with the mean kinetic energy, ⟨E K ⟩, provide key insights into the hydrogen local environment to rationalize the puzzling feature of liquid water near the triple point. DINS is the unique experimental technique that directly access the n(p). 18 The basic principles of data interpretation of the DINS technique are based on the validity of the impulse approximation (IA), 19 which is exact in the limit of infinite momentum transfer, ℏq. 20,21 Within the IA, the inelastic neutron sc...

Section: Toc Graphicsupporting

confidence: 84%

Direct Measurements of Quantum Kinetic Energy Tensor in Stable and Metastable Water near the Triple Point: An Experimental Benchmark

Andreani

Senesi

2016

J. Phys. Chem. Lett.

“…Dark-blue diamonds refer to data around density maximum [76]; dark blue squares at 271 and 300 K from ref. [77]; and dark-blue triangles refer to the present data.…”

Section: -6supporting

confidence: 54%

The onset of the tetrabonded structure in liquid water

Corsaro

Mallamace

Sci. China Phys. Mech. Astron.

et al. 2019

Water properties are dominated by the hydrogen bond interaction that gives rise in the stable liquid phase to the formation of a dynamical network. The latter drives the water thermodynamics and is at the origin of its well known anomalies. The HB structural geometry and its changes remain uncertain and still are challenging research subjects. A key question is the role and effects of the HB tetrahedral structure on the local arrangement of neighboring molecules in water. Here the hydrogen dynamics in bulk water is studied through the combined use of Neutron Compton Scattering and NMR techniques. Results are discussed in the framework of previous studies performed in a wide temperature range, in the liquid, solid, and amorphous states. For the first time this combined studies provide an experimental evidence of the onset of the water tetrahedral network at T∼315 K, originally proposed in previous studies of transport coefficients and thermodynamical data; below this temperature the local order in water changes and the lifetime of local hydrogen bond network becomes long enough to gradually develop the characteristic tetrahedral network of water. water, neutron compton scattering, NMR

“…In the second parametric approach, one uses a model function for J(y,Q), i .e., a spherically averaged multivariate Gaussian [36,[58][59][60][61][62]. The basic assumption in this case is that the NMD of each individual particle is well approximated by a multivariate Gaussian distribution with three distinct frequencies ω x,y,z associated with local and orientationdependent principal axes of the molecule.…”

Section: Momentum Distributions and Mean Kinetic Energiesmentioning

confidence: 99%

“…As far as water is concerned, DINS is currently a quantitative and well-established technique capable to get fresh insights into the intermolecular HB interactions at the heart of the peculiar properties of water, in many respects complementary to INS and optical spectroscopy [62,141]. The most significant results of these investigations are reviewed in the following sections.…”

Section: Water From the Bulk To The Nanoscalementioning

confidence: 99%

Electron-volt neutron spectroscopy: beyond fundamental systems

Andreani

Krzystyniak

et al. 2017

Advances in Physics

141

This work provides an up-to-date account of the use of electron-volt neutron spectroscopy in materials research. This is a growing area of neutron science, capitalising upon the unique insights provided by epithermal neutrons on the behaviour and properties of an increasing number of complex materials. As such, the present work builds upon the aims and scope of a previous contribution to this journal back in 2005, whose primary focus was on a detailed description of the theoretical foundations of the technique and their application to fundamental systems [see Andreani et al., Adv. Phys. 54 (2005) p.377] A lot has happened since then, and this review intends to capture such progress in the field. With both expert and novice in mind, we start by presenting the general principles underpinning the technique and discuss recent conceptual and methodological developments. We emphasise the increasing use of the technique as a non-invasive spectroscopic probe with intrinsic mass selectivity, as well as the concurrent use of neutron diffraction and first-principles computational materials modelling to guide and interpret experiments. To illustrate the state of the art, we discuss in detail a number of recent exemplars, chosen to highlight the use of electron-volt neutron spectroscopy across physics, chemistry, biology, and materials science. These include: hydrides and proton conductors for energy applications; protons, deuterons, and oxygen atoms in bulk water; aqueous protons confined in nanoporous silicas, carbon nanotubes, and graphene-related materials; hydrated water in proteins and DNA; and the uptake of molecular hydrogen by soft nanostructured media, promising materials for energy-storage applications. For the primary benefit of the novice, this last case study is presented in a pedagogical and question-driven fashion, in the hope that it will stimulate further work into uncharted territory by newcomers to the field. All along, we emphasise the increasing (and much-needed) synergy between experiments using electron-volt neutrons and contemporary condensed matter theory and materials modelling to compute and ultimately understand neutron-scattering observables, as well as their relation to materials properties not amenable to scrutiny using other experimental probes