Inelastic Incoherent Neutron Scattering Spectra 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.

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.

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]

Neutron Spectroscopy of Norbornane

Results of inelastic incoherent neutron scattering (IINS) on norbornane are reported. The IINS spectra in the low-temperature phases display low-frequency internal vibration modes very well. The assignment of these modes is proposed in reference to the results of the calculations of the structure and dynamics of isolated molecules by semi-empirical quantum chemistry methods.

Progesterone and testosterone studies by neutron-scattering methods and quantum chemistry calculations

Inelastic incoherent neutron scattering (IINS) and neutron diffraction spectra of progesterone and testosterone were measured simultaneously on the NERA spectrometer at the IBR-2 pulsed reactor in Dubna. Both studied samples do not indicate any phase transition in the temperature range from 20 to 290 K. The IINS spectra have been transformed to the phonon density of states (PDS) in the one-phonon scattering approximation. The PDS spectra display well-resolved peaks of low-frequency internal vibration modes up to 600 cm-1. The assignment of these modes was proposed taking into account the results of calculations of the structure and dynamics of isolated molecules of the investigated substances. The quantum chemistry calculations were performed by the semi-empirical PM3 method and at the restricted Hartree–Fock level with the 6-31* basis set. The lower internal modes assigned to torsional vibration of the androstane skeleton mix with the lattice vibrations. The intense bands in the PDS spectra in the frequency range from 150 to 300 cm-1 are related to librations of structurally inequivalent methyl groups.

Neutron spectroscopic study of hydrogen bonding dynamics in l-serine

Inelastic incoherent neutron scattering (IINS) spectra were obtained at 10 K for normal and deuterated l-serine. The geometry of l-serine molecule was optimized for the zwitterion form using ab initio HF, MP2 and DFT (B3LYP) levels with 6-31G* and 6-311++G** basis sets. The theoretical frequencies of normal and d 4- l-serine were compared with IINS spectra. Normal coordinate analysis and band assignments based on ab initio calculations and experimental data were presented. IINS frequencies due to the out-of-plane γ(N–H…O) hydrogen bond motions were observed and identified.

Neutron scattering, infra red, Raman spectroscopy and ab initio study of l-threonine

Inelastic incoherent neutron scattering spectra (IINS) were obtained for normal and deuterated l-threonine. Raman and infrared spectra were also recorded. Geometries were optimized for the zwitterion form using ab initio Hartree-Fock (HF) levels with 6–31G*, 6–311G*, 6–311G** and 6–311++G** basis sets. Force fields and normal modes were calculated and used as basis for an assignment of the spectral features.

Phase Transitions and Water Dynamics of [Mn(H2O)6](ClO4 )2 Studied by Differential Scanning Calorimetry and Neutron Scattering Methods

Abstract DSC measurements performed at 95 -290 K have shown that [Mn(H 2 O) 6 ](CIO 4) 2 possesses, besides a high-temperature phase, existing above 323 K, four low-temperature solid phases. The inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) pat-terns registered at 20 -290 K have supported the DSC results and provided evidence that the investigated substance possesses even more than five solid phases. The IINS spectra have shown that in the room-temperature phase, water molecules perform fast stochastic reorientation at the picosecond scale. The orientational disorder characteristic for the room-temperature phase can be easily overcooled and frozen. Even by relatively slow cooling at ca. 40 K/hour a metastable, orientational (protonic) glass phase is formed below ca. 160 K. Below ca. 100 K, a structural phase transition was observed by the NPD, however the IINS spectra indicate existence of the pure ordered low-temperature phase only after annealing the sample for a few hours at 100 K. On heating, a structural phase transition takes place at ca. 120 K, and at ca. 225 K water molecules begin fast reorientation.

Vibrational spectra of the adduct of 1,8-bis(dimethylamino)naphthalene with dichloromaleic acid (DMAN · DCM)

The infra-red (IR), Raman (R) and inelastic incoherent neutron scattering (IINS) spectra, particularly in low frequency region, of the title ionic adduct were studied. It is shown that all low frequency vibrations (below 200 cm −1) of (CH 3) 2N groups of protonated 1,8-bis(dimethylamino)naphthalene (DMAN) — clearly observed in IINS spectra — are sensitive to the environment, i.e. to the type of counterion forming short contacts with CH bonds of methyl groups. The internal frequencies were also calculated by ab initio method. The results are consistent with numerous observations of the counteranion effect on the geometry of the protonated DMAN. The conclusions are compared with structural and NMR studies reported recently for the 1,8-bis(dimethylamino)naphthalene with dichloromaleic acid (DMAN · DCM) adduct. The single crystal R polarized spectra taken over the frequency range 20–3200 cm −1 were analyzed in detail. We have shown that a substantial difference in the IR spectrum of the dichloromaleic acid (DCM) anion in the DMAN adduct and in the potassium salt results from different geometries of OHO hydrogen bonds. In the case of potassium salt the chains of longer intermolecular hydrogen bonds are formed described by means of a double minimum potential.

Neutron-scattering investigation of ammonium dynamics in (NH 4) 2− xRb xSO 4 mixed salts

Inelastic incoherent neutron-scattering (IINS) investigations of the mixed salts (NH 4) 2− x Rb x SO 4 for the whole concentration range, 0.0 ⩽ x ⩽ 2.0, have been performed on the NERA spectrometer at the IBR-2 pulsed reactor in Dubna. The IINS spectra show that ammonium ions undergo fast reorientations even in the ferroelectric phase; however, for (NH 4) 2SO 4, the rotational barrier slightly decreases at the phase transition. In the mixed salts, this effect vanishes with increasing rubidium concentration and above x > 0.4, the stochastic dynamics of the ammonium ions do not depend on the ferroelectric transition. Upon cooling to low temperatures, the ammonium ions form a substitutional protonic glass, within x ranging from approx. 0.4 to 1.2. At high rubidium concentrations, the IINS spectra display the localized dynamics of NH 4 (II), which occupy type II crystallographic position.

The IINS spectroscopy of amino acids: l-isoleucine

Results of inelastic incoherent neutron scattering (IINS) supplemented by infrared (IR) and Raman scattering studies on normal and N-deuterated l-isoleucine in the energy transfer up to 800 cm −1 are reported. The IINS spectra of l-isoleucine show additional bands as compared to the spectra obtained by optical spectroscopic methods. In both, normal and d 3- l-isoleucine, extra bands correspond to out-of-plane γ(N–H⋯O) (518, 505, 250 cm −1) and γ(N–DO⋯O) (362 cm −1) hydrogen bond vibrations. Methyl and carboxyl groups vibrations are observed at 219, 228, 250, 281 cm −1 and 175, 543, 686, 749 cm −1 respectively.

Dynamics investigations of the proton conductor 12-tungstophosphoric acid by neutron scattering

Compared with other spectroscopic techniques, the method of inelastic incoherent neutron scattering (IINS), owing to extraordinary large cross-section of hydrogen for incoherent scattering, has great advantages in the investigation of the dynamics of protons in compound where they are surrounded by heavy atoms. For proton conductors, this technique enables the identification of various protonic species, determination of their dynamics, as well as the dynamics of heavy atoms to a measure in which they are bonded to hydrogen. Here we discuss the IINS spectra obtained with a pulsed neutron source, during the dehydration process of 12-tungstophosphoric acid 6-hydrate (H5O2)3 *(PW12O40).

Neutron scattering studies on structural phase transitions of superionic conductor Cs HSO4

Abstract The results of neutron diffraction (ND) and inelastic incoherent neutron scattering (IINS) studies on phase transitions and vibrational spectra in superionic conductor CsHSO4 at pulsed reactor IBR-2 are reported. It is shown that in the temperature range 123–420 K there are three phases (III, II, I) in CsHSO4 crystal and only two phases (II, I) in partly deuterated Cs(D0.7H0.3)SO4 crystal. The unit cell parameters in monoclinic phase II by ND on single crystal are determined. A considerable change in IINS spectra in superionic phase I says for a disorded state of protons in the lattice in this phase.