Incoherent Inelastic Neutron Research Articles

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.

Computationally Supported Neutron Scattering Study of Parent and Chemically Reduced Graphene Oxide

Synthetic graphene oxide (GO) as well as the product of its reducing performed in the regime of hydrogenolysis (rGO) were studied by both elastic and inelastic neutron scattering at low and room temperature conditions. The neutron diffraction patterns were analyzed to confirm stacking structures of both species consisting of 2–3 and ∼7 layers of microsize lateral dimension and the interlayer distances of 7 and 3.5 A, respectively. The inelastic incoherent neutron scattering spectra were analyzed in the frame of the computationally supported one-phonon amplitude-weighted density of vibrational states G(ω) approximation. Calculations of G(ω) spectra were performed in the framework of semilocal density functional theory. The computational models were adjusted to the atom mass content of both GO and rGO species. The presented study has revealed the retained water in the freshly made GO, corresponding to the relatively low humidity, which further reacts with the oxygen-containing groups at the GO basal planes....

Hydrogen self-dynamics in liquid H(2)-D(2) mixtures studied through inelastic neutron scattering.

We have measured the dynamic structure factor of liquid para-hydrogen mixed with normal deuterium (T=20 K) at two different concentration levels using incoherent inelastic neutron scattering. This choice has been made since the presence of D(2} modifies the self-dynamics of H(2) in a highly nontrivial way, acting both on its pseudophononic and its diffusive parts in a tunable way. After an accurate data reduction, recorded neutron spectra were studied through the modified Young and Koppel model and the H(2) center-of-mass self-dynamics structure factor was finally extracted for the two mixtures. Some physical quantities (i.e., self-diffusion coefficient and mean kinetic energy) were determined and compared with accurate quantum calculations, which, in addition, also provided estimates of the velocity autocorrelation function for the H(2) centers of mass. These estimates, in conjunction with the Gaussian approximation, were used to simulate the H(2) center-of-mass self-dynamics structure factor in the same range as the experimental one. The agreement between measured and calculated spectra was globally good, but some discrepancies proved the unquestionable breakdown of the Gaussian approximation in these semiquantum systems at a level comparable to that already observed in pure liquid para-hydrogen.

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.

Quantumness of correlations and Maxwell's demon in molecular excitations created by neutron scattering

Nonclassical correlations known as entanglement, quantum discord, quantum deficit, measurement‐induced disturbance, quantum Maxwell's demon, etc., may provide novel insights into quantum‐information processing, quantum‐thermodynamics processes, open‐system dynamics, quantum molecular dynamics, and general quantum chemistry. We study a new effect of quantumness of correlations accompanying collision of two distinguishable quantum systems A and B, the latter being part of a larger (interacting) system B + D. In contrast to the common assumption of a classical environment or “demon” D, the quantum case exhibits striking new qualitative features. Here, in the context of incoherent inelastic neutron scattering from H‐atoms which create molecular excitations (vibration, rotation, translation), we report theoretical and experimental evidence of a new phenomenon: a considerably reduced effective mass of H, or equivalently, an anomalous momentum‐transfer deficit in the neutron‐H collision. These findings contradict conventional theoretical expectations even qualitatively, but find a straightforward interpretation in the new theoretical frame under consideration. © 2015 Wiley Periodicals, Inc.

Inelastic and elastic neutron scattering studies of the vibrational and reorientational dynamics, crystal structure and solid–solid phase transition in [Mn(OS(CH3)2)6](ClO4)2 supported by theoretical (DFT) calculations

The vibrational and reorientational dynamics of CH3 groups from (CH3)2SO ligands in the high- and low-temperature phases of [Mn(OS(CH3)2)6](ClO4)2 were investigated by quasielastic and inelastic incoherent neutron scattering (QENS and IINS) methods. The results show that above the phase transition temperature (detected earlier by differential scanning calorimetry (DSC) at TC5c=222.9K on cooling and at TC5h=225.4K on heating) the CH3 groups perform fast (τR≈10−12–10−13s) reorientational motions. These motions start to slow down below TC5c Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS and IINS, indicated that this phase transition is associated with a change of the crystal structure, too. Theoretical infrared absorption, Raman and inelastic incoherent neutron scattering spectra were calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on C, H, S, O atoms) for the isolated equilibrium model (isolated [Mn(DMSO)6]2+ cation and ClO4− anion). Calculated spectra show a good agreement with the experimental spectra (FT-IR, RS and IINS). The comparison of the results obtained by these complementary methods was made.

Understanding the packing in the 1 : 1 molecular complex 1,3,5-tricyanobenzene–hexamethylbenzene by probing lattice modes

Inelastic neutron scattering is used to directly probe the effect of intermolecular interactions in the text-book co-crystal hexamethylbenzene : tricyanobenzene.

An inelastic incoherent neutron scattering study of the internal dynamics of ergocalciferol and cholesterol

A model of the methyl group dynamics of two steroid compounds: cholesterol and ergocalciferol was proposed on the grounds of complementary studies performed by inelastic incoherent neutron scattering, nuclear magnetic resonance and quantum chemistry calculation methods.

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.

Inelastic incoherent neutron scattering study of the molecular properties of pure hydrogen peroxide and its water mixtures of different concentration.

We have investigated the spectra of shock-frozen H2O2-H2O mixtures across the full composition range 99.1%-0.0% H2O2. In contrast to literature reports, we find that intermediate compositions (30%-70% H2O2) freeze to a solid solution rather than phase separating, which only occurs on annealing to just below the melting point. We have fully characterised the dihydrate H2O2·2H2O (48.6% H2O2) for the first time and shown that its spectrum can account for the features previously observed on the surface of a Au/TiO2 catalyst.

Does a Dry Protein Undergo a Glass Transition?

Bovine serum albumin (BSA) with extremely low hydration level 0.04, which is usually defined as dry, has been investigated in the temperature range between 200 and 340 K by incoherent inelastic neutron scattering using the neutron time-of-flight spectrometer FOCUS (PSI, Switzerland). Anomalous temperature behavior has been revealed for relaxational and low-frequency vibrational dynamics of BSA in the vicinity of 250 K. The mean-square atomic displacement has been shown to exhibit a change in the slope of temperature dependence near the same temperature. The presented results point out that the glass-like transition occurs in the dry protein.

Polymorphism of Paracetamol: A New Understanding of Molecular Flexibility through Local Methyl Dynamics

This study focuses on the interplay of molecular flexibility and hydrogen bonding manifested in the monoclinic (form I) and orthorhombic (form II) polymorphs of paracetamol. By means of incoherent inelastic neutron scattering and density functional theory calculations, the relaxation processes related to the methyl side-group reorientation were analyzed in detail. Our computational study demonstrates the importance of considering quantum effects to explain how methyl reorientations and subtle conformational changes of the molecule are intertwined. Indeed, by analyzing the quasi elastic signal of the neutron data, we were able to show a unique and complex motional flexibility in form II, reflected by a coupling between the methyl and the phenyl reorientation. This is associated with a higher energy barrier of the methyl rotation and a lower Gibbs free energy when compared to form I. We put forward the idea that correlating solubility and molecular flexibility, through the relation between pKa and methyl rotation activation energy, might bring new insights to understanding and predicting drug bioavailability.

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.

New observations on hydrogen bonding in ice by density functional theory simulations

In this paper, we report on a series of computational simulations on hydrogen bonding in two ice phases (Ih and Ic) using CASTEP with PW91 and RPBE exchange—correlation based on ab initio density functional theory. The strength of the H-bond is correlated with intramolecular O—H stretching, and the energy splitting exists for both the H-bond and covalent O—H stretching. By analyzing the dispersion relationship of ω(q), we observe the separation of the longitudinal optic (LO) mode from transverse optic (TO) mode at the gamma point, seemingly interpreting the controversial two H-bond peaks in the vibrational spectrum of ice recorded by inelastic incoherent neutron scattering experiments. The test of ambient environment on phonon density of sates (PDOS) shows that the relaxed tetrahedral structure is the most stable structural configuration for water clusters.

Crystal structure of two [Ba(H2O)3](ClO4)2 phases and H2O ligands reorientational motions studied by X-ray single crystal, inelastic and quasielastic incoherent neutron scattering and proton magnetic resonance

XRSCD and NPD measurements indicated that the crystal space group (P63/m) is the same for high and low temperature phases. IINS spectra calculated by the DFT method are in a good agreement with the experimental data. The QENS peaks, registered at 225 and 175K, (above and below the phase transition at TCh=211.3K, respectively) do not show any broadening, what implies that the corresponding reorientational correlation times for 180° jumps of H2O ligands are longer than 10–11s. The 1H NMR line absorption results indicate that above TCh, the ratio of the area under the narrow contribution of the line to the whole line is close to 1:3, what suggests that upon heating of the sample, activation of a much faster than 10−8s rotational (of diffusive nature) motion of the only one of the three H2O ligands per one [Ba(H2O)3](ClO4)2 formula unit occurs.

Molecular flexibility and structural instabilities in crystalline l-methionine

We have investigated the dynamics in polycrystalline samples of l-methionine related to the structural transition at about 307K by incoherent inelastic and quasielastic neutron scattering, X-ray powder diffraction as well as ab-initio calculations. l-Methionine is a sulfur amino acid which can be considered a derivative of alanine with the alanine R-group CH3 exchanged by CH3S(CH2)2. Using X-ray powder diffraction we have observed at ~190K an anomalous drop of the c-lattice parameter and an abrupt change of the β-monoclinic angle that could be correlated to the anomalies observed in previous specific heat measurements. Distinct changes in the quasielastic region of the neutron spectra are interpreted as being due to the onset and slowing-down of reorientational motions of the CH3–S group, are clearly distinguished above 130K in crystalline l-methionine. Large-amplitude motions observed at low frequencies are also activated above 275K, while other well-defined vibrations are damped. The ensemble of our results suggests that the crystalline structure of l-methionine is dynamically highly disordered above 275K, and such disorder can be linked to the flexibility of the molecular thiol-ether group.

Hydrogen trapping at dislocation cores at room temperature in deformed Pd

Abstract Small-angle neutron scattering (SANS) measurements of hydrogen segregation at dislocations in heavily deformed single crystal Pd have been performed at very low solute concentration (PdH0.0016) at equilibrium with respect to hydrogen gas at 295 K. The net (the without-hydrogen measurement subtracted from with-hydrogen measurement) absolute differential macroscopic scattering cross section has been fit with a cylindrical form factor to represent the Cottrell atmosphere, yielding local trapped concentration δ ∼ 0.06 [H]/[Pd], local volumetric dilatation f ∼ 1.01, and trapping radius R ∼ 4 A of the segregated hydrogen. This measurement augments SANS results below ambient temperature [B.J. Heuser, H. Ju, Phys. Rev. B 83 (2011) 094103]. The temperature dependence of the measured radius is confirmed by a Fourier transform of hydrogen occupation at dislocations based on an elastic continuum treatment [Trinkle et al., Phys. Rev. B 83 (2011) 174116]. The measured trapping parameters are consistent with a depopulation of weak long-range dislocation strain fields at ambient temperature; hydrogen binding to stronger core dislocation sites persists at 295 K and results in the measured net scattering. The local solute concentration and trapping radius (less than two Burgers vectors in Pd), are both too small to support optic mode dispersion due to inter-hydrogen interactions. This result supports the conclusion that trapped hydrogen undergoes a hydride to solid solution phase transformation between 200 and 300 K based on hydrogen vibration density of states measurements using incoherent inelastic neutron scattering [Trinkle et al., Phys. Rev. B 83 (2011) 174116, Ju et al., Nucl. Instr. Meth. Phys. Res. A 654, (2011) 522, and Heuser et al., Phys. Rev. B 78 (2008) 214101].