Incoherent Inelastic Neutron Scattering Research Articles

The vibrations of hydrogen bonds

I present recent inelastic incoherent neutron scattering (INS) work involving the study of the H-bond vibrations. These vibrations have spectral consequences which are strongly dependent upon spectroscopic technique, and these will be indicated for IR and Raman, and detailed for INS. The vibrational dynamics of the simple FHF − will be used by way of an example. These INS results demonstrate that the latest generation of neutron spectrometers provides new insights into H-bonding dynamics.

An inelastic incoherent neutron scattering study of ice II, IX, V, and VI—in the range from 2 to 140 meV

Inelastic incoherent neutron scattering (IINS) cross sections have been measured for the recovered high-pressure phases of ice, ices II, V, VI, and IX (H2O) and ices II and IX (D2O) in the energy range from 2 to 150 meV at 20 K using the TFXA (time-focused crystal analyzer) neutron spectrometer on the ISIS pulsed neutron source at the Rutherford-Appleton Laboratory. The excellent resolution of the TFXA (less than 2%) covers the whole range of translational and librational modes for the ices investigated and enables us to identify the fine structures in their spectra. Hence a direct comparison between the amplitude-weighted phonon density of states derived from the experimental spectrum and from a lattice dynamic calculation is possible [E. Whalley and J. E. Bertie, J. Chem. Phys. 46, 1271 (1967); J. E. Bertie and E. Whalley, ibid. 40, 1646 (1964)]. The spectra from these polymorphic ices show many new features in the translational region, which are not visible using infared and Raman techniques. In the librational band region, the general features vary remarkably between phases. Thus, for instance, ice II, in which the protons are ordered, shows more structure in this region and has a sharper low-energy cutoff than do the other phases examined. The most significant observation is that the low-energy cutoff is characteristic of the phase. Relative to ice Ih, there is a shift of 4.3 meV for ice IX, of 8.8 meV for ice II, 8.6 meV for ice V, and 12.2 meV for ice VI.

Layered proton conducting trivalent metal acid sulphates: intercalation reactions, characterisation by incoherent inelastic neutron scattering and exafs spectroscopies

Members of the series of acid salts HM(III)(SO 4) 2· nH 2O, n=1 or 4, M(III)=Al, Fe, In, etc., are protonic conductors ( σ=10 -4-10 -5 ω -1 cm -1 at 25° C) of pronounced two-dimensional structure. Hydrated proton species intercalated between the anionic layers [M(SO 4) 22H 2O] - n have been identified by incoherent inelastic neutron scattering (IINS) spectroscopy. HFe(SO 4) 2·4H 2O is a promising ion exchange and intercalation agent. The products of its redox reactions with lithium, sodium, ammonium and zinc ions have been investigated by IINS and extended X-ray absorption fine structure spectroscopies.

Water Motion in Harmotome – Studied by Incoherent Inelastic and Quasielastic Neutron Scattering

AbstractThe mobility of the water molecules in the natural zeolite harmotome Ba2[(AlO2)4(SiO2)12] · 12H2O has been studied by incoherent neutron scattering on powder samples in several dehydration states and at different temperatures. – The external vibrational modes of the water molecules were determined from the inelastic part of the spectra (energy transfers 5 < ΔE < 100 meV) and were assigned to translational and rotational vibrations. The diffusive motion of water was evaluated from the quasielastic scattering and values of the residence time τ0 = 2.9 – 5.5 · 10−12 s, diffusion constant D = 5.0–25·10−5 cm2/s and mean jump length 〈I〉 = 0.41–0.66 nm were derived. – The results from the neutron scattering experiments were interpreted based on a redetermination of the crystal structure.

Synthesis, characterization and inelastic neutron scattering spectra of hydrogen insertion compounds of the mixed [formula omitted] oxide V 9Mo 6O 40

Hydrogen insertion compounds of V 9Mo 6O 40 have been synthesized and investigated using incoherent inelastic neutron scattering (IINS) vibrational spectroscopy. IINS spectra of H xV 9Mo 6O 40 (x=7.8 and 17.5) confirm that in both phases H is present as coordinated hydroxyl groups. There is no evidence for the presence of coordinated water in contrast to the hydrogen insertion compounds of MoO 3 and V 2O 5.

Low‐Temperature Structure and Lattice Dynamics of 4,4′,‐Difluorobiphenyl

AbstractPhonon frequencies in the centre of the Brillouin zone, dispersion relations, and phonon density of states are calculated for 4,4′‐difluorobiphenyl, following structure investigations by means of X‐ray diffraction on a monocrystalline sample at 110 K. The resulting phonon density of states, weighted with the amplitudes of hydrogen atom vibrations are compared with that obtained from the inelastic incoherent neutron scattering (IINS) data. From the calculated dispersion relations it can be inferred that the incommensurate phase transition (well established in isostructural biphenyl) does not occur in 4,4′‐difluorobiphenyl.

The Phonon Spectra of Ordered and Disordered Phases of MBBA

Abstract The spectra of inelastic incoherent neutron scattering (IINS) in the methoxy-benzilidene-butylaniline (MBBA) have been measured with the simultaneous phase control of the sample using the neutron diffraction (ND). The experiments were carried out in the nematic liquid crystal state (NLC) at T = 300 K as well as in seven solid modifications in the temperature range from 90K to 290K. The variety of polymorphous transformations in the MBBA (an amorphous state C0, two disordered solid state mesophases C1 and C2, four ordered crystalline phases C3 C4, C5 C6) enabled us to trace the transformation of the vibrational spectrum at the transition from amorphous into crystalline state. For solid state modifications the weighted density of phonon states has been obtained. In the disordered phases (C0 and C1) as compared with the crystalline ones the Debye approximation is applicable for a narrower frequency range, and an increasing excess of the phonon density of state is observed in the low frequency range.

Debye-Waller factor through the glass transition temperature in a-selenium, by incoherent inelastic neutron scattering

We report, in this work, Incoherent Inelastic Neutron Scattering (IINS) measurements in amorphous bulk selenium. Taking into account the low frequency Vibrational Density-of-States(VDOS), we study the modification introduced in the Debye-Waller factor by increasing temperature through the glass transition temperature ( T g ). The occurrence, in the vibrational density-of-states, of a ω 2 dependence in the acoustic region, allowed us to apply the Debye theory from which the variations of the Deybe-Waller factor are calculated in addition. It is shown that the main contribution to it is given by the acoustic region of the vibrational density of states and has a faster increase for temperatures above T g .

The inelastic neutron scattering spectrum of chloroform in solution

The incoherent inelastic neutron scattering (INS) spectrum of CHCl 3 in liquid SO 2 (ambient temperature) in the region 0–3600 cm −1 is presented. For the first time it has been demonstrated that good quality INS data on solutes can be obtained over this energy transfer range. A discussion of suitable solvents for further work is included.

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.

Neutron scattering study of NiH x at 77K

The results of simultaneous measurements of inelastic incoherent neutron scattering (IINS) and neutron diffraction on NiH x system with x = 0.40, 0.28 and 0.12 at temperatures of 77 K are briefly presented. In the phonon density of states, supposing a one-phonon mechanism for the scattering process, the optic modes appear as a broad band from 70 to 140 meV with a strong peak at 90 meV and weak peaks at 105 and 130 meV. Neutron diffraction confirms information about the phase composition of the samples investigated.

The vibrational spectra of H 3O + and H 5O +2 ions in HUO 2PO 4 · 4H 2O

Infrared and incoherent inelastic neutron-scattering (IINS) spectra of HUO 2HPO 4 · 4H 2O (HUP) are presented and found to be consistent with the presence of both H 3O + and H 5O + 2 ions. Spectral evidence for these ions is more pronounced in the IINS than the infrared spectrum. A normal-coordinate treatment suggests that the H 5O + 2 ion in HUP should be regarded as a trapped proton, vibrationally coupled to a limited number of modes of two water molecules — where these modes contain a significant component parallel to the bridging structure.

Debye-Waller factors in incoherent inelastic neutron scattering spectra of molecular polycrystals

The incoherent inelastic neutron scattering (IINS) spectrum of HCCo3(CO)9 has been obtained in order to test some present methods of calculating band intensities for polycrystalline samples. The fundamental and first overtones of the carbon-hydrogen bending mode were observed at 860 and 1712 cm-1 respectively. The C-H stretching mode was observed at 3041 cm-1 and this is the first report of the observation of such a mode in which there is no possibility of confusion with overtone and combination bands.

Inelastic neutron scattering spectra of some English coals: a preliminary study

The applications of incoherent inelastic neutron scattering (IINS) spectroscopy to the study of coal are discussed in the light of preliminary data (350–2000 cm −1) obtained from three English coals of various ranks.

Inelastic neutron scattering study of low frequency motions in [Co(C 5H 5) 2+] and [Cr(C 6 H 62+] intercalated in the MnPS 3 layered compound

The incoherent inelastic neutron scattering (INS) spectra of Mn 0.84PS 3[Co(C 5H 5) 2] 0.32 and Mn 0.86 PS 3[Cr(C 6H 6) 2] 0.28 compounds at 10 K have been investigated within the frequency ranges 0–80 cm −1 ( E 0 = 12.5 meV) and 0–360 cm −1 ( E 0 = 50 meV). Also, infrared and Raman spectra (0–400 cm −1 of Cr(C 6H 6) 2I at various temperatures have been obtained for the first time. From a comparison of far infrared, low frequency Raman and INS results, we propose an assignment for the internal torsion and for the librational motions in the intercalated organometallic cations. An estimate of the potential barrier height against the torsion and the R′ z whole-body rotation is derived; these values are compared with those calculated for the corresponding iodide salts. We conclude that a significant decrease of the intermolecular forces acting on the rings is taking place within the interlamellar space.

Inelastic Incoherent Neutron Scattering as an Alternative Method to Investigate Local Critical Behavior

Inelastic Incoherent Neutron Scattering as an Alternative Method to Investigate Local Critical Behavior