Incoherent Inelastic Neutron Scattering Research Articles

Quantum thermodynamics of hydrogen in nano-structured materials—H2 in carbon nanotubes

Abstract Modern quantum theory of correlations predicts, and reveals, new counter-intuitive dynamical effects of hydrogen in nano-structured materials, being of considerable importance for basic research as well as for technological applications. To support this claim, here the focus is on H2 molecules in carbon nanotubes and other nanocavities, as experimentally investigated with the well established technique of incoherent inelastic neutron scattering (INS). In particular, the experimentally determined momentum and energy transfers from an H2 molecule in a carbon (C-) nanotube resulting in roto-translational motion along the nanotube axis, appear to (1) either violate the standard conservations laws, or (2) attribute the translating H2 molecule a highly reduced inertia, as quantified by the effective mass M eff ≈ 0.64 a.m.u. (atomic mass units), instead of 2 a.m.u. for an isolated molecule. This counter-intuitive INS-observation has no conventional interpretation, but it can be qualitatively interpreted “from first principles” in the frame of modern theories of quantumness of correlations and Quantum Thermodynamics (QTD). This analysis also provides a surprising new physical insight: The nano-structured cavities do represent quantum systems which contribute to the quantum dynamics of the hydrogen translational dynamics, and thus to the hydrogen transport in the studied materials. This insight may also have far-reaching consequences for technological applications and material sciences (e.g. fuel cells, H storage materials, etc.), since it concerns the choice and design of “optimized” materials adsorbing or carrying hydrogen.

Spectroscopic Identification of Hydrogen Bond Vibrations and Quasi-Isostructural Polymorphism in N-Salicylideneaniline.

The ortho-hydroxy aryl Schiff base 2-[(E)-(phenylimino)methyl]phenol and its deutero-derivative have been studied by the inelastic incoherent neutron scattering (IINS), infrared (IR) and Raman experimental methods, as well as by Density Functional Theory (DFT) and Density-Functional Perturbation Theory (DFPT) simulations. The assignments of vibrational modes within the 3500–50 cm−1 spectral region made it possible to state that the strong hydrogen bond in the studied compound can be classified as the so-called quasi-aromatic bond. The isotopic substitution supplemented by the results of DFT calculations allowed us to identify vibrational bands associated with all five major hydrogen bond vibrations. Quasi-isostructural polymorphism of 2-[(E)-(phenylimino)methyl]phenol (SA) and 2-[(E)-(phenyl-D5-imino)methyl]phenol (SA-C6D5) has been studied by powder X-ray diffraction in the 20–320 K temperature range.

Polymorphism and Conformational Equilibrium of Nitro-Acetophenone in Solid State and under Matrix Conditions.

Conformational and polymorphic states in the nitro-derivative of o-hydroxy acetophenone have been studied by experimental and theoretical methods. The potential energy curves for the rotation of the nitro group and isomerization of the hydroxyl group have been calculated by density functional theory (DFT) to estimate the barriers of the conformational changes. Two polymorphic forms of the studied compound were obtained by the slow and fast evaporation of polar and non-polar solutions, respectively. Both of the polymorphs were investigated by Infrared-Red (IR) and Raman spectroscopy, Incoherent Inelastic Neutron Scattering (IINS), X-ray diffraction, nuclear quadrupole resonance spectroscopy (NQR), differential scanning calorimetry (DSC) and density functional theory (DFT) methods. In one of the polymorphs, the existence of a phase transition was shown. The position of the nitro group and its impact on the crystal cell of the studied compound were analyzed. The conformational equilibrium determined by the reorientation of the hydroxyl group was observed under argon matrix isolation. An analysis of vibrational spectra was achieved for the interpretation of conformational equilibrium. The infrared spectra were measured in a wide temperature range to reveal the spectral bands that were the most sensitive to the phase transition and conformational equilibrium. The results showed the interrelations between intramolecular processes and macroscopic phenomena in the studied compound.

Proton Dynamics in Palladium-Silver: An Inelastic Neutron Scattering Investigation.

Proton dynamics in Pd77Ag23 membranes is investigated by means of various neutron spectroscopic techniques, namely Quasi Elastic Neutron Scattering, Incoherent Inelastic Neutron Scattering, Neutron Transmission, and Deep Inelastic Neutron Scattering. Measurements carried out at the ISIS spallation neutron source using OSIRIS, MARI and VESUVIO spectrometers were performed at pressures of 1, 2, and 4 bar, and temperatures in the 330–673 K range. The energy interval spanned by the different instruments provides information on the proton dynamics in a time scale ranging from about 102 to 10−4 ps. The main finding is that the macroscopic diffusion process is determined by microscopic jump diffusion. In addition, the vibrational density of states of the H atoms in the metal lattice has been determined for a number of H concentrations and temperatures. These measurements follow a series of neutron diffraction experiments performed on the same sample and thus provide a complementary information for a thorough description of structural and dynamical properties of H-loaded Pd-Ag membranes.

Symmetry/Asymmetry of the NHN Hydrogen Bond in Protonated 1,8-Bis(dimethylamino)naphthalene

Experimental and theoretical results are presented based on vibrational spectra and motional dynamics of 1,8-bis(dimethylamino)naphthalene (DMAN) and its protonated forms (DMANH+ and the DMANH+ HSO4− complex). The studies of these compounds have been performed in the gas phase and solid-state. Spectroscopic investigations were carried out by infrared spectroscopy (IR), Raman, and incoherent inelastic neutron scattering (IINS) experimental methods. Density functional theory (DFT) and Car–Parrinello molecular dynamics (CPMD) methods were applied to support our experimental findings. The fundamental investigations of hydrogen bridge vibrations were accomplished on the basis of isotopic substitutions (NH → ND). Special attention was paid to the bridged proton dynamics in the DMANH+ complex, which was found to be affected by interactions with the HSO4− anion.

Inter- vs. Intramolecular Hydrogen Bond Patterns and Proton Dynamics in Nitrophthalic Acid Associates.

Noncovalent interactions are among the main tools of molecular engineering. Rational molecular design requires knowledge about a result of interplay between given structural moieties within a given phase state. We herein report a study of intra- and intermolecular interactions of 3-nitrophthalic and 4-nitrophthalic acids in the gas, liquid, and solid phases. A combination of the Infrared, Raman, Nuclear Magnetic Resonance, and Incoherent Inelastic Neutron Scattering spectroscopies and the Car–Parrinello Molecular Dynamics and Density Functional Theory calculations was used. This integrated approach made it possible to assess the balance of repulsive and attractive intramolecular interactions between adjacent carboxyl groups as well as to study the dependence of this balance on steric confinement and the effect of this balance on intermolecular interactions of the carboxyl groups.

Weak Values and Quantum Information in Scattering Physics — New Theoretical and Experimental Effects

Weak Values (WV) and Two-State-Vector Formalism (TSVF) provide novel insights in various quantum physical and technological fields. In the first part of the paper we consider a new quantum effect of scattering accompanying an elementary collision of two quantum systems A and B, in which the latter interacts with a quantum environment. In clear contrast to a classical environment, the quantum case can exhibit counter-intuitive effects of momentum- and energy-transfer which contradict conventional expectations. Experimental evidence of a new effect—deficit of momentum transfer (equivalently: reduced effective mass) in a neutron-atom collision—is presented and theoretically interpreted. Here, non-relativistic incoherent inelastic neutron scattering (INS) is applied. INS on single H2 molecules confined in multi-walled carbon nanotube channels has been experimentally investigated. Interpreted within conventional theory, the results reveal a counter-intuitive reduced effective mass of the recoiling H2 molecule, i.e. M = 0.64 a.m.u. (atomic mass units). In contrast, this finding has a simple qualitative interpretation within WV and TSVF theory. In the second part of the paper we report on current experimental and theoretical investigations in the field of X-ray diffraction (XRD), which belongs to coherent scattering. Preliminary XRD results from cubic crystalline materials show a surprising variation of the measured lattice parameter (usually called “lattice constant”) with momentum transfer. A first theoretical model of the effect in the light of the new theory is presented. These findings give further evidence for the broad character and significance of the novel WV and TSVF theory.

Effects of Quantum Confinement of Hydrogen in Nanocavities – Experimental INS Results and New Insights

Current developments of non-relativistic quantum mechanics appear to predict, and reveal, counter-intuitive dynamical effects of hydrogen in nanostructured materials that are of considerable importance for basic research as well as for technological applications. In this review, the experimental focus is on HO and H molecules in carbon nanotubes and other nanocavities that have been experimentally investigated using the well-established technique of incoherent inelastic neutron scattering (INS). For instance, the momentum and energy transfers, as obtained from the commonly used standard data analysis techniques, from a (I) H2 molecule in a C-nanotube resulting in a roto-translational motion along the nanotube axis seems to (1) either violate the standard conservation laws or (2) to attribute to the H molecule undergoing translation the effective mass a.m.u. (atomic mass units) instead of the expected 2 a.m.u. A similar striking anomalous effect has been found in the neutron-H scattering from the (II) H2O molecules in nano-channels of some solid materials, in which O-H stretching vibrations along the channel axis are created. The results of this scattering process seem to once again either violate the standard conservation laws or to attribute to the effective mass of the struck H2 molecule as a.m.u. instead of the expected value of 1 a.m.u. We show that these counterintuitive observations from the INS studies have no conventional interpretation within the standard non-relativistic scattering theory. However, they can be qualitatively interpreted “from first principles” within the framework of modern theories of (III) time-symmetric quantum dynamics, as provided by the weak values (WV) and two-state- vector formalism (TSVF), and/or (IV) quantum correlations, especially quantum discord (QD) and quantum thermodynamics (QTD). The theoretical analysis provides an intuitive understanding of the experimental results, gives strong evidence that the nano-structured cavities do represent quantum systems which participate significantly in the dynamics of the neutron-H scattering, and, surprisingly, shows that new physical information can be derived from the experimental data. This latter point may also have far-reaching consequences for technology and material sciences (e.g., fuel cells, H storage materials, etc.). Moreover, novel insights into the short-lived quantum dynamics and/or quantum information theory can be gained.

Weak Values and Two-State Vector Formalism in Elementary Scattering and Reflectivity—A New Effect

The notions of Weak Value (WV) and Two-State Vector Formalism (TSVF), firstly introduced by Aharonov and collaborators, provide a quantum-theoretical formalism of extracting new information from a system in the limit of small disturbances to its state. Here, we explore two applications to the case of non-relativistic two-body scattering with one body weakly interacting with its environment. We present a physically compelling analysis of a new quantum effect: momentum transfer deficit and an accompanying enhanced energy transfer; or, equivalently, an apparent mass-deficit of the struck body. First, incoherent inelastic neutron scattering (INS) from protons of H 2 molecules in C-nanotubes is investigated. The data of the H 2 translational motion along the nanotube shows that the neutron apparently exchanges energy and momentum with a fictitious particle with mass of 0.64 atomic mass units (a.m.u.), which is in blatant contradiction with the expected value of 2 a.m.u. Second, the same theory is applied to neutron reflectivity—which is elastic and coherent—from the interface of (single crystal) Si with H 2 O-D 2 O liquid mixtures. The data shows a striking enhanced reflectivity in a wide range of momentum transfers, which is tantamount to a momentum-transfer deficit with respect to conventional expectations. However, these effects find a natural interpretation within the WV-TSVF theoretical analysis under consideration. In summary, both scattering effects contradict conventional theoretical expectations, thus also supporting the novelty of the theoretical framework of WV and TVSF. Additionally, it should be pointed out that the two dynamical variables in the interaction Hamiltonian of the theoretical model belong to two different physical bodies.

Raman light scattering, infrared absorption and neutron scattering studies of the phase transition and reorientational dynamics of H2O ligands and ClO4↙ anions in [Ca(H2O)4](ClO4)2

Vibrational-reorientational dynamics of H2O ligands and ClO4↙ anions in the high-, intermediate- and low-temperature phases of [Ca(H2O)4](ClO4)2, detected previously by differential scanning calorimetry (DSC) method, were investigated. The following experimental methods were applied to achieve the goal: middle-infrared (FT-MIR), Raman spectroscopy (RS) and inelastic incoherent neutron scattering (IINS). FT-MIR and RS spectra versus temperature show distinct changes in full-width-at-half-maximum (FWHM) of some bands connected with vibrational modes of ClO4↙ and [Ca(H2O)4]2+ ions. It suggests that in the high temperature phase these ions (and also the ligands from complex cation) perform fast (picoseconds correlation time scale, which is characteristic for optical spectroscopy) stochastic reorientational motions, however in the lower temperatures the speed of these motions is slowed down. Moreover, the splitting of some bands accompanying the observed phase transitions. The comparison of the results obtained by these complementary methods was made. Additionally, IR, RS and IINS spectra were calculated by the DFT method and an excellent agreement with the experimental data was obtained using CASTEP plane-wave periodic boundary condition code. The bands were assigned based on analysis of the phonon eigenvectors obtained from CASTEP calculations.

Water Signatures and Their Thermal Stability in Bedded Salt for Nuclear Waste Storage: An Incoherent Inelastic Neutron Spectroscopy Study

The forms of water and their thermal stability in bedded salt are crucial in determining the material's suitability for heat-generating nuclear waste storage. Here we show first-of-its-kind incoherent inelastic neutron scattering (IINS) results of bedded salts to distinguish three water environments: intergranular water molecules confined to grain boundaries, water trapped as brine in fluid inclusions, and structural water in intracrystalline hydrous minerals. Sixteen spectral lines can be distinguished unambiguously in the 0-1100 cm(-1) multiphonon and librational domain, yielding an unprecedented high resolution for a natural material. The spectral response to temperature illustrates the bimodality of the technique enabling the intergranular water component to be distinguished from that of brine, shedding light on a nearly 30-year-old problem in characterizing different forms of water in rock salt. This pioneering study shows that IINS provides insight into the cause and effect of moisture migration and its coupling to thermomechanical properties in salt formations. Our results are pertinent to subsurface energy exploration and storage, including nuclear waste storage, in salts. (Less)

General Selection Rule in the Inelastic Neutron Scattering Spectroscopy of a Diatomic Molecule Confined Inside a Near-Spherical Nanocavity.

Knowledge of the relevant selection rules is crucial for the accurate interpretation of experimental spectra in general. There has been a consensus for a long time that the incoherent inelastic neutron scattering (INS) spectroscopy of the vibrations of discrete molecular compunds is free from any selection rules. We contradict this widely held view by presenting an analytical derivation of the general selection rule for the INS spectroscopy of a hydrogen molecule inside a near-spherical nanocavity. It defines all forbidden transitions, originating in a range of initial translation-rotation (TR) states, ground and excited, of the caged para- and ortho-H2, as well as HD, that are unobservable in the INS spectra. These predictions are amenable to experimental verification. In addition, we demonstrate that the general selection rule applies to the INS spectroscopy of any diatomic molecule in a nanocavity with near-spherical symmetry, which exhibits strong TR coupling. Its existence strongly suggests that similar selection rules apply to the INS spectra of other molecular and supramolecular systems, and need to be identified.

Mixed quantum/classical approach to OH-stretch inelastic incoherent neutron scattering spectroscopy for ambient and supercooled liquid water and ice Ih.

OH-stretch inelastic incoherent neutron scattering (IINS) has been measured to determine the vibrational density of states (VDOS) in the OH-stretch region for liquid water, supercooled water, and ice Ih, providing complementary information to IR and Raman spectroscopies about hydrogen bonding in these phases. In this work, we extend the combined electronic-structure/molecular-dynamics (ES/MD) method, originally developed by Skinner and co-workers to simulate OH-stretch IR and Raman spectra, to the calculation of IINS spectra with small k values. The agreement between theory and experiment in the limit k → 0 is reasonable, further validating the reliability of the ES/MD method in simulating OH-stretch spectroscopy in condensed phases. The connections and differences between IINS and IR spectra are analyzed to illustrate the advantages of IINS over IR in estimating the OH-stretch VDOS.

Maxwell’s Demon Observing Creation of a Molecular Vibration

Quantum correlations and associated quantum information concepts (e. g. quantum discord, entanglement, quantum Maxwell’s demon) provide novel insights in various quantum-information processing tasks, quantum-thermodynamics processes, open-system dynamics, quantum molecular dynamics, and general many-body physics. We investigate a new effect of correlations accompanying collision of two quantum systems A and B, the latter being part of a larger (interacting) system B+D. In contrast to the usual case of a classical ‘environment’ or ‘demon’ (which can have only classical correlations with A+B during and after the collision), the quantum case exhibits striking new features. Here, in the frame of incoherent inelastic neutron scattering (INS) and vibrational dynamics of molecules, we report experimental evidence of a new phenomenon: quantum deficit of momentum transfer in an elementary neutron-molecule collision, in particular, in INS from single H2O molecules confined in channels with sub-nanometer diameter. The INS findings are in clear contrast to conventional theoretical expectations, but are naturally (albeit qualitative) interpreted in the frame of modern theory of quantumness of correlations, thus also proposing a new operational meaning of quantum discord and related measures.

Vibrational dynamics in dendridic oligoarylamines by Raman spectroscopy and incoherent inelastic neutron scattering.

Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C-H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C-C and C-N deformation modes with those of C-H nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation.

Vibrations and reorientations of H2O molecules in [Sr(H2O)6]Cl2 studied by Raman light scattering, incoherent inelastic neutron scattering and proton magnetic resonance

Vibrational–reorientational dynamics of H2O ligands in the high- and low-temperature phases of [Sr(H2O)6]Cl2 was investigated by Raman Spectroscopy (RS), proton magnetic resonance (1H NMR), quasielastic and inelastic incoherent Neutron Scattering (QENS and IINS) methods. Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS, did not indicated a change of the crystal structure at the phase transition (detected earlier by differential scanning calorimetry (DSC) at TCh=252.9K (on heating) and at TCc=226.5K (on cooling)). Temperature dependence of the full-width at half-maximum (FWHM) of νs(OH) band at ca. 3248cm−1 in the RS spectra indicated small discontinuity in the vicinity of phase transition temperature, what suggests that the observed phase transition may be associated with a change of the H2O reorientational dynamics. However, an activation energy value (Ea) for the reorientational motions of H2O ligands in both phases is nearly the same and equals to ca. 8 kJmol−1. The QENS peaks, registered for low temperature phase do not show any broadening. However, in the high temperature phase a small QENS broadening is clearly visible, what implies that the reorientational dynamics of H2O ligands undergoes a change at the phase transition. 1H NMR line is a superposition of two powder Pake doublets, differentiated by a dipolar broadening, suggesting that there are two types of the water molecules in the crystal lattice of [Sr(H2O)6]Cl2 which are structurally not equivalent average distances between the interacting protons are: 1.39 and 1.18Å. However, their reorientational dynamics is very similar (τc=3.3⋅10−10s). Activation energies for the reorientational motion of these both kinds of H2O ligands have nearly the same values in an experimental error limit: and equal to ca. 40kJmole−1. The phase transition is not seen in the 1H NMR spectra temperature dependencies. Infrared (IR), Raman (RS) and inelastic incoherent neutron scattering (IINS) spectra were calculated by the DFT method and quite a good agreement with the experimental data was obtained.

First principles calculations and experiments for Cu-Mg/Li hydrides negative electrodes

ABSTRACTWe have studied CuLi0.08Mg1.92 and determined that the compound reacts with hydrogen to form CuLi0.08Mg1.92H5 [1]. Additionally, we have proposed the compound as a negative electrode material which is the main purpose of the present study. Moreover, we have observed that the latter compound acts as a catalyst in the formation of MgH2, LiH, TiH2 [2] and hydrogen desorption. In this work, first principles and phonon calculations were performed in order to establish the reactions occurring at the negative electrode of a Li conversion battery in presence of CuLi0.08Mg1.92H5 and (Li) – solid solution of Mg in Li – approximately Li2Mg3. We have calculated the minimum theoretical specific capacity to be 1156 mAh/g (for an anode with 100% of CuLi0.08Mg1.92H5) and the △Eeq = 0.81 V (vs. Li+/Li) at 298 K. Furthermore, we have determined all the reactions occurring in the referred system and its sequence using Inelastic Incoherent Neutron Scattering (IINS) and X-Ray Diffraction (XRD).

Understanding Vibrational Anharmonicity and Phonon Dispersion in Solid Ammonia Borane

We compute the hydrogen vibrational spectra for bulk ammonia borane (NH3BH3), for both protonated and deuterated cases, using harmonic and anharmonic methodologies as well as low frequency coupling and quantifying dispersive effects to understand their influence on the resulting spectra. Even at 10 K the accounting of anharmonic effects on the incoherent inelastic neutron scattering (IINS) signal is more significant than approximations introduced by sampling and interpolating a finite simulation cell to capture dispersion effects. We compare our computed anharmonic spectrum with IINS measurements and find excellent agreement.

Comparison of FANS and ARCS incoherent inelastic neutron scattering measurements of hydrogen trapped at dislocations in deformed Pd

Incoherent inelastic neutron scattering (IINS) measurements of the vibrational density of states (VDOS) of hydrogen trapped at dislocations in deformed PdH 0.0013 have been performed using ARCS at the SNS and FANS at the NCNR. A comparison of data sets at 4 and 295 K indicates good agreement of the measured VDOS for the two instruments. The low hydrogen inventory (∼10 -3 g) provides a test of the response of each instrument over the energy transfer range of 40–100 meV corresponding to the vibrational density of states of the hydrogen modes.

Hydrogen Vibrational Excitation Spectra of CaF<SUB>2</SUB>-Type Metal Hydrides Synthesized from Ti-Based BCC Solid Solution Alloys

Hydrogen vibrational excitation was studied for CaF2-type metal hydrides synthesized from Ti-based BCC solid solution alloys using inelastic incoherent neutron scattering (IINS). Ti1:0V1:1Mn0:9H4:5 and Ti0:7V1:2Cr1:1H4:8 showed IINS spectra similar to that reported for TiH2. The first three peaks were isolated but the higher excitation peaks were not clear. Analysis of the spectra using curve-fitting with Gauss functions revealed that the hydrogen vibration of Ti1:0V1:1Mn0:9H4:5 is harmonic but that of the Ti0:7V1:2Cr1:1H4:8 is deviated from harmonic, which reflects a trumpet-type potential. The relation between metal-hydrogen distance and vibrational excitation energy for the above two hydrides and Ti1:1Cr1:4Mo0:3H 5 was compared with a series of CaF2-type binary metal hydrides. All the hydrides of the Ti-based alloys had lower vibrational excitation energies than the binary metal hydrides for the corresponding metal-hydrogen distances. [doi:10.2320/matertrans.MA201014]