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

Phase transitions, structural changes and molecular motions in [Zn(NH 3) 4](BF 4) 2 studied by neutron scattering, X-ray powder diffraction and nuclear magnetic resonance

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.

Phase transition, molecular motions, structural changes and low-frequency vibrations in [Cu(NH 3) 5](ClO 4) 2

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.

Dynamics of NH3 ligands and ClO4− anions in the phase transition in [Cd(NH3)6](ClO4)2 studied by x-ray powder diffraction, neutron scattering methods and infrared spectroscopy

Inelastic Incoherent Neutron Scattering in Catalysis Research

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

Phase transitions and H2O motions in [Ca(H2O)4](NO3)2 studied by infrared spectroscopy, inelastic/quasi-elastic incoherent neutron scattering and proton magnetic resonance, Part II

The purpose of the present investigation was to utilize the inelastic incoherent neutron scattering (INS) technique to reveal changes at the surface of technical catalysts under the influence of hydrogen in gas/solid interactions and during chemical reactions in a liquid-phase process. The formation and the properties of supported palladium hydride and changes of the hydrogen-related surface chemistry of the corresponding activated carbon supports in 20% Pd/C catalysts after short-term and long-term hydrogen cycling at different hydrogen pressures and temperatures were studied. The spectra indicate that hydrogenation of the activated carbon support by hydrogen spillover occurs to, partly, give a material that strongly resembles a-C:H (amorphous hydrogenated carbon). Indications for different relaxation phenomena and long-range phase coherence inside of supported particles of palladium hydride compared to hydrogenated palladium black were obtained. A 5% Pd/C catalyst after use in C-C coupling reactions, the Heck reaction of bromobenzene and styrene to stilbenes, was also studied after subsequent solvent extraction. Evidence for a preferential adsorption and accumulation of cis-stilbene at the catalyst surface was obtained. INS allows identification of a certain isomer from a complex reaction mixture preferentially adsorbed at the surface of a finely divided industrial heterogeneous catalyst.

The (NH4)3H(SO4)2 and [(NH4)0.82Rb0.18]3H(SO4)2 crystals are investigated by dielectric spectroscopy, inelastic incoherent neutron scattering (IINS), and neutron powder diffraction. A comparative analysis of the data obtained is given. It is shown that the phase transitions II ↔ III, III ↔ IV, IV ↔ V, and V ↔ VII in the (NH4)3H(SO4)2 crystal are accompanied by changes in the orientation ordering of the NH4+ ions. In the [(NH4)0.82Rb0.18]3H(SO4)2 crystal, these phase transitions are completely suppressed and the long-range order inherent in the II phase is retained over the entire temperature range covered (6–300 K). It is revealed that this crystal at the temperature Tg≈70 K undergoes a transition to the dipole glass phase, which is attended by “freezing” the orientation disordering of the ammonium ions.

Detailed spectroscopic studies performed by quasi-elastic and inelastic light scattering (Rayleigh wing and Raman) and a preliminary analysis by quasi-elastic and inelastic neutron scattering (incoherent quasi-elastic neutron scattering (IQENS) and incoherent inelastic neutron scattering (IINS)) in water, in the bulk and in confined geometry at different hydration levels and at room temperature, are presented. The possibility to compare the experimental results obtained by both the complementary spectroscopic techniques and analysed in the framework of existing models for confined liquids, has allowed us to identify the clear influence of the confinement on the mobility of this fundamental liquid, which shows a dramatic frozen-in effect with respect to the bulk state. In addition, the presence of an α-relaxation process, related to a distribution of relaxational times which recalls the mode coupling theory (MCT), characteristic of dense supercooled liquids, has been confirmed. Furthermore inelastic features in both spectroscopies show a loss of low frequency collective vibrational bands connected with the presence of tetrahedral environments for physisorbed water. Finally Raman results show a systematic lowering of the OH stretching bands for water involved in tetrahedral C2v symmetry.

Vibrational and reorientational dynamics and thermal properties in [Mg(H2O)4](ReO4)2 supported by periodic DFT study

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.

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.

The interaction between water and some of amino acids (glycine, L-glutamine, L-threonine, L-cysteine and L-serine) was studied by inelastic incoherent neutron scattering (IINS). The vibrational spectra of dry amino acids and amino acids with a water content (e.g., 1 mol water/1 mol amino acid) were recorded. Comparing the difference spectra obtained by subtracting the spectrum of dry sample from those of wet sample with the spectra of ice Ih, we obtained that the difference spectrum for serine changed greatly from normal ice spectrum; but on the other hand, the difference spectra for the other amino acids such as glycine, glutamine, threonine, and cysteine changed slightly. The results demonstrate that serine has stronger hydrophilic character than glycine, glutamine, threonine, and cysteine. This is the first time the hydrophilic or hydrophobic character of amino acids was studied by using inelastic neutron scattering techniques, which provides important information for theoretical modeling and force field refinement for the interaction between water and the amino acids studied here.