Symmetric Bending Mode Research Articles

Effect of oxygen content on the 29Si NMR, Raman spectra and oxide ion conductivity of the apatite series, La8+xSr2−x(SiO4)6O2+x/2

29Si NMR data have been recorded for the apatite series La8+xSr2-x(SiO4)6O2+x/2 (0 < or = x < or = 1.0). For x = 0, a single NMR peak is observed at a chemical shift of approximately -77 ppm, while as the La : Sr ratio and hence interstitial oxygen content is increased, a second peak at a chemical shift of approximately -80 ppm is observed, which has been attributed to silicate groups neighbouring interstitial oxide ions. An increase in the intensity of this second peak is observed with increasing x, consistent with an increase in interstitial oxide ion content, and the data are used to estimate the level of interstitial oxide ions, and hence Frenkel-type disorder in these materials. The increase in second 29Si NMR peak intensity/interstitial oxide ion content is also shown to correlate with an increase in conductivity. The effect of interstitial oxygen content can also be studied by means of Raman spectroscopy, with a new mode at 360 cm(-1) appearing for samples with x > 0 in the symmetric bending mode energy region of the SiO4 group. The intensity of this mode increases with increasing oxygen content, yielding results comparable to those from the NMR studies, showing the complementarities of the two techniques.

Thermally induced conformational and structural disordering in polyethylene crystal studied by near-infrared spectroscopy

Thermally induced structural and conformational changes in polyethylene (PE) samples were explored by using near-infrared (NIR) spectroscopy. The differences in the temperature-dependent structural disordering process among six PE samples were depicted by monitoring the intensities of NIR bands characteristic of orthorhombic crystalline phase. The temperature dependency of bands in the NIR region that have been considered to be due to orthorhombic crystalline lattice was compared to that of a band at 1378cm−1 due to the methyl symmetric bending mode. The intensity decrease of the band in the mid-infrared (MIR) region seems to sensitively reflect the overall disordering of orthorhombic crystalline structure. As a result of this study, the intensity decrease of the bands in the NIR spectral region was found to proceed at lower temperature than that of the band at 1378cm−1. This finding suggests the status of orthorhombic crystalline structure probed by the intensity of the band at 1378cm−1 and that by the “crystalline” bands in the NIR spectral region may not be identical. The NIR spectra were further analyzed by two-dimensional (2D) correlation spectroscopy to provide the in-depth analysis of NIR bands. The 2D correlation spectroscopy has detected the presence of two NIR bands at 4342 and 4290cm−1 due to orthorhombic crystalline phase and those at 5840 and 5640cm−1 due to amorphous phase. The hetero-spectral 2D correlation analysis was carried out between the NIR spectral region of 4365–4240cm−1 and the well-established MIR spectral region for CH2 wagging deformation region of 1390–1240cm−1, where bands due to nonplanar conformer are detected. This approach allowed us to determine NIR bands, which behave in a way similar to MIR bands originating from conformational defect sequences that exist in the orthorhombic crystalline lattice, the amorphous domain and the chain fold regions. As a result of the hetero-spectral 2D NIR–MIR correlation spectroscopic studies on the development of conformational defect sequence in three types of PE samples, it was concluded that the intensity of a band at 4265cm−1 changes in the same manner as the MIR bands at 1368, 1353 and 1308cm−1 assignable to gtg, gg and gtg′ (kink) conformations. This finding means that the state of conformational disorder in PE crystal can be studied by monitoring the intensity of the NIR band at 4265cm−1. The use of NIR spectroscopy makes it possible to directly probe the degree in the formation of conformational defect sequences in thick PE products typically produced in industry, which cannot be studied by MIR spectroscopy. This paper thus provides in-depth fundamental understandings on NIR spectra of PE as well as the results of our study regarding structural and conformational changes in PE crystals probed by NIR spectroscopy.

Raman spectroscopic study of the phase transitions and pseudospin phonon coupling in sodium ammonium sulphate dihydrate

This work reports a detailed study of the temperature dependence of the lattice dynamics of single crystal sodium ammonium sulphate dihydrate (SASD) obtained from polarized Raman scattering. The phase transitions in SASD are marked by the appearance of new weak bands and anomalies in the temperature dependence of wave number and damping factor of several lattice and internal modes. The temperature dependence of the symmetric bending modes of ammonium ion as well as the abrupt shift of wave number of some lattice and internal modes related to the molecular units point to a proton ordering mechanism associated with the paraelectric-ferroelectric phase transition. The anomalies, which have been detected in the temperature dependence of the wave number and of the damping coefficient of some external and internal modes, are well described by a theoretical model that takes into account the coupling between pseudospins and phonons.

New floating floor design with optimum isolator location

In this paper, a new design concept of an isolated honeycomb floor with a special arrangement of isolators is proposed to improve the vibration isolation performance of conventional lightweight cement floor panels in the frequency range of 120–600 Hz. The symmetric bending resonance frequencies and mode shapes of a honeycomb floor panel were identified by a shaker test. The effects on vibration isolation of isolator position and acoustic insulation were then investigated using experimental modal analysis. The analysis suggests that four design features ensure the optimum vibration isolation performance of a square floating honeycomb floor: the floor panel should be small, stiff, and lightweight; the isolators must be placed at the nodal points of the symmetric bending modes of the floor panel; the vibration must be transmitted via the center point of the floor panel; and acoustic insulation material should be installed inside the cavity. The proposed floating floor design achieved a vibration reduction of 20–30 dB in the frequency range of 120–600 Hz. In addition, the proposed floor was found to have a 20 dB lower vibration level at the first bending resonance frequency than the conventional design with isolators that are placed at the edges.

Monosodium glutamate in its anhydrous and monohydrate form: Differentiation by Raman spectroscopies and density functional calculations

Monosodium glutamate (MSG), a common flavor enhancer, is detected in aqueous solutions by Raman and surface-enhanced Raman (SERS) spectroscopies at the micromolar level. The presence of different species, such as protonated and unprotonated MSG, is demonstrated by concentration and pH dependent Raman and SERS experiments. In particular, the symmetric bending modes of the amino group and the stretching modes of the carboxy moiety are employed as marker bands. The protonation of the NH 2 group at acidic pH values, for example, is detected in the Raman spectra. From the measured SERS spectra, a strong chemical interaction of MSG with the colloidal particles is deduced and a geometry of MSG adsorbed on the silver surface is proposed. In order to assign the observed Raman bands, calculations employing density functional theory (DFT) were performed. The calculated geometries, harmonic vibrational wavenumbers and Raman scattering activities for both MSG forms are in good agreement with experimental data. The set of theoretical data enables a complete vibrational assignment of the experimentally detected Raman spectra and the differentiation between the anhydrous and monohydrate forms of MSG.

Infrared Study of the Interaction of Charged Silica Particles with TiO2 Particles Containing Adsorbed Cationic and Anionic Polyelectrolytes

Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was used to study the adsorption of charged silica particles onto TiO(2) particles coated with anionic sodium polyacrylate (NaPA) or cationic poly(diallyldimethylammonium) chloride (PDADMAC). To the best of our knowledge, this is the first time that IR spectroscopy has been used to study the interaction of a polymer layer on one particle with a second different particle. The results show that, once adsorbed on the TiO(2) particle, the PDADMAC or the NaPA does not transfer to the silica particles. In the case of NaPA coated TiO(2), positively charged silica particles deposit on the TiO(2) and this is accompanied by a change in the relative intensities of the bands due to COOH and COO(-) groups. From this change in band intensity, it is calculated that only approximately 6% of the COO(-) groups located in the loops and tails bind to the silica particle. This shows that the polymer bridges the two particles through an electrostatic interaction with the outer COO(-) groups. Similarly, in the case of the TiO(2) particles coated with PDADMAC, negatively charged silica deposits on the TiO(2) and this is accompanied by an increase in intensity of the symmetric bending mode of the (+)N(CH(3))(3) group. This change in band intensity arises from the binding of these cationic sites of the polymer to the negative surface sites on the silica.

Raman spectroscopic detection of wyartite in the presence of rabejacite

AbstractRaman microscopy was used to confirm the presence of wyartite, CaU5+(UO2)2(CO3)O4(OH)(H2O)7, in the presence of rabejacite, (Ca(UO2)4(SO4)2(OH)5·6H2O), obtained from the Ranger Mine, Northern Territory, Australia. This occurrence is unusual in that it means that a uranyl carbonate has been formed under acidic conditions. Wyartite is a mineral known for the occurrence of pentavalent U5+. A band is observed at 818 cm−1 in the Raman spectrum of wyartite assigned to the ν2 symmetric bending mode of the (CO3)2− units. The presence of carbonate is confirmed by the ν1 stretching vibration at 1071 cm−1 and the ν3 stretching vibrations at 1445 and 1345 cm−1. Two bands are observed at 853 and 837 cm−1 and are assigned to the ν1 stretching modes of the UO2 units. Raman spectroscopy allows the partial band separation of the ν2 (CO3)2− and ν1 modes of UO2. The Raman spectrum of rabejacite is characterized by an intense sharp band at 1010 cm−1 assigned to the ν1 stretching mode of (SO4)2−. Three bands observed at 1086, 1123 and 1175 cm−1 are attributed to the ν3 antisymmetric stretching modes of (SO4)2−. The mineral rabejacite is also characterized by ν2 bending modes at 457 and 394 cm−1 and ν4 bending modes at 666, 605, 537 and 505 cm−1. Raman spectroscopy has proven most useful for the detection of wyartite in the presence of other mineral phases. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Single‐crystal Raman study of erythrite, Co3(AsO4)2·8H2O

AbstractSingle‐crystal Raman and infrared spectra of natural and synthetic erythrite, Co3(AsO4)2·8H2O, are reported and compared with the spectra polycrystalline, synthetic annabergite, Ni3(AsO4)2·8H2O, and hörnesite, Mg3(AsO4)2·8H2O. Factor group analysis and single‐crystal considerations were used to interpret the experimental data. The Raman spectra of erythrite reveal the ν1 arsenate stretching vibration at 850 cm−1 (Ag) with the corresponding infrared band at 821 cm−1 (Bu). The ν3 antisymmetric vibration is split into three components, observed at 796 (Ag), 788 (Ag) and 803 (Bg) cm−1. The ν2 symmetric bending modes are observed at 375 (Ag) and 385 (Bg) cm−1. The ν4 bending modes are predicted to split into three bands which are observed at 441 (Ag), 446 (Bg) and 457 (Ag) cm−1. Lattice vibrations are found at 112 (Ag), 124 (Bg), 145 (Ag), 157 (Bg), 165 (Ag), 179 (Ag), 189 (Ag), 191 (Bg), 201 (Bg), 210 (Ag), 227 (Ag), 250 (Ag), 264 (Ag), 264 (Ag), 280 (Bg), 302 (Bg), 321 (Bg) and 338 cm−1(Ag). Hydroxyl stretching modes are observed at 3050, 3218, 3333, 3449 and 3479 cm−1 in the infrared spectrum. Raman‐active hydroxyl bands are detected at 3009 (Bg), 3052 (Ag), 3190 (Bg) 3203 (Bg), 3281 (Ag) and 3310 (Bg), 3436 (Bg) and 3443 (Ag) cm−1. Infrared hydroxyl bands at 3050 and 3218 cm−1 are from water type II, short hydrogen bonding distances, and the bands at 3449 and 3479 cm−1 are due to water I, long hydrogen bonding distances. Water bending modes are detected in the infrared spectrum at 1571, 1621, 1641 and 1682 cm−1, but owing to the inherent weak Raman scattering cross‐section of water these could not be detected in the Raman spectra. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Spectroscopic Identification and Dynamics of Adsorbed Cetyltrimethylammonium Bromide Structures on TiO2 Surfaces

Infrared spectroscopy is used to identify the aggregated structures of adsorbed cetyltrimethylammonium bromide (CTAB) on negatively charged TiO2 surfaces. In particular, there are abrupt changes in the intensity of the symmetric bending mode of the CTAB headgroup, and these abrupt changes have been correlated to different aggregated structures along the adsorption isotherm. Furthermore, by measuring spectra as a function of time, it is possible to obtain information on the dynamics of the formation of aggregated CTAB structures on the surface. It is shown that aggregated hemimicellar, admicellar, and micellar structures initially adsorb through intermediate structures that have a higher percentage of CTAB molecules bound directly to charged sites on the surface. Above the critical micelle concentration (cmc), the CTAB exists as micelles on the surface when exposed to a bare TiO2 surface or to a TiO2 surface already covered with hemimicellar/admicellar adsorbed structures. In the latter case, the existing ...

Matrix isolation infrared spectroscopic investigation of the coordination chemistry and reactivity of OVF 3

The matrix isolation technique has been combined with infrared spectroscopy to identify and characterize the product of the codeposition of OVF 3 with NH 3 and with a series of nitrogen and oxygen donor bases into argon matrices at 14 K. This codeposition led to the formation of the isolated 1:1 complexes between OVF 3 and these bases. Each complex was characterized spectroscopically, including strong shifts to the V–F stretching modes, and a lesser shift to the VO stretching mode. Numerous perturbed vibrational modes of the base subunits were noted, including a strong, 230 cm −1 blue shift to the symmetric bending mode of NH 3. The magnitudes of these shifts indicate that OVF 3 is a moderate strength Lewis acid. However, in contrast to analogous reactions with OVCl 3, no further thermal or photochemical transformations of the complex occurred. Theoretical calculations were also carried out in support of the experimental work.

Infrared Spectrum of the H3N−HCl Complex in Solid Ne, Ne/Ar, Ar, and Kr. Matrix Effects on a Strong Hydrogen-Bonded Complex

Ammonia and hydrogen chloride vapors from thermal decomposition of NH4Cl co-deposited with excess neon at 4−5 K formed the H3N−HCl complex. Strong, broad 2084 cm-1 and strong, sharp 1060.2 cm-1 absorptions are assigned to the H−Cl stretching and symmetric NH3 bending modes and weaker 2017.4 and 708.9 cm-1 bands to the overtone of the NH3 mode and the H−Cl librational fundamental of the 1:1 complex. Complementary experiments were done with neon/argon mixtures, argon, and krypton to investigate the 1:1 complex in a range of matrix environments. Vibrational assignments are supported by 15NH4Cl, ND4Cl, and 15ND4Cl isotopic substitution. The neon matrix spectrum suggests a strong hydrogen bond, slightly stronger than in the gas-phase complex, but not as strong as found in the argon and krypton matrix hosts owing to increased solvation by the more polarizable matrix atoms.

Pathways to double ionization of atoms in strong fields

We discuss the final stages of double ionization of atoms in a strong linearly polarized laser field within a classical model. We propose that all trajectories leading to nonsequential double ionization pass close to a saddle in the phase space that we identify and characterize. The saddle lies in a two degree of freedom subspace of symmetrically escaping electrons. The distribution of a longitudinal momenta of ions as calculated within the subspace shows the double hump structure observed in experiments. Including a symmetric bending mode of the electrons allows us to reproduce the transverse ion momenta. We discuss also a path to sequential ionization and show that it does not lead to the observed momentum distributions.

Ft-Raman Study of Three Synthetic Solid Solutions Formed by Orthorhombic Sulfates: Celestite-Barytes, Barytes-Anglesite and Celestite-Anglesite

In the present work, three different solid solutions whose end-members are the orthorhombic sulfates celestite (SrSO4), barytes (BaSO4) and anglesite (PbSO4) are studied using FT-Raman spectroscopy. Sulfate anion symmetric internal modes have been examined in detail by means of band-shape analysis and component fitting procedures. the symmetric stretching mode v1(A1) changes its wavenumber position linearly with the cationic composition of the samples which further confirms the ideal character of the solid solutions studied. the corresponding full-width at half-height is strongly increased in the central components of the different solid solutions which can be understood as an effect of the positional disorder induced by random cationic substitution. Similar results are observed in the symmetric bending mode, v2 (E). the study of the low frequency spectral region permits one to differentiate translational modes of the sulfate anion, which changes its wavenumber position when the alkali-earth metal ion changes from rotational modes. This permits the tentative band assignment of the anglesite rotational Raman bands at 134 and 152 cm−1, which were previously not assigned.

Nonlinear vibration modes of an elastic panel under periodic loading

The dynamic instability and nonlinear behavior of a nonshallow thin elastic cylindrical panel with simply supported rectilinear edges under uniformly distributed periodic load is studied. The regions of regular and chaotic dynamics are determined for symmetric and nonsymmetric bending modes of the panel. It is shown that depending on the external load frequency, the nonsymmetric buckling. which occurs when the load amplitude reaches a critical value, can lead to two different dynamic modes.

Ammoniated Ammonium Ions Studied Theoretically and Experimentally, ab initio Calculation and Tandem Mass Spectrometer Experiments.

Ammoniated ammonium ions (NH4+·nNH3, n=0-6) were studied theoretically by molecular orbital calculations and experimentally by observing their formation and decomposition in a corona discharge-jet expansion process. Ab initio calculations were carried out by employing Gaussian 98 program, which gave optimized structures, binding energies, and wave numbers of the symmetric bending mode of the solvent ammonia molecule. Effects of the stagnation pressure of reactant gas and the diameter of the gas expanding pinhole were examined on the size distribution of NH4+·nNH3. It was found that the cluster size n in NH4+·nNH3 increased by one or remained unchanged in the jet expansion process. Effects of discharge current, the pinhole diameter and flight time were examined on the decomposition rate of the ammonia cluster ions. It was deduced that the internal energies of the cluster were mainly determined by the reactions involved in the cluster formation or decomposition.

Raman and infrared microscopy study of zunyite, a natural Al 13 silicate

Zunyites, Al 13Si 5O 20(OH,F) 18Cl, have been studied by Raman and infrared microscopy. The infrared spectrum (700–4000 cm −1) is characterised by a band near 720 cm −1 and a quintet of bands at 890, 992, 1062, 1130 and 1176 cm −1. The first two bands are assigned to Al–OH deformation modes with the 992 cm −1 mode being infrared inactive and the latter three bands as Si–O symmetric stretching modes. The IR hydroxyl-stretching region shows three Al–OH stretching modes at 3313 cm −1 with a shoulder at ±3200 cm −1 and a low intensity band at ±3623 cm −1. The Raman hydroxyl-stretching region reveals seven bands corresponding with Al–OH modes at ±3634, 3431, 3374, 3354, 3337, 3320 and 3306 cm −1. The corresponding Al–OH deformation modes are observed at 930, 950 and 994 cm −1. In the Raman spectral region of 1000–1300 cm −1, Si–O–Si symmetric stretching modes are observed at 1067, 1101 and 1126 cm −1, from which the middle band is infrared inactive and therefore assigned to the 180° intertetrahedral Si–O–Si bond. The remaining bands at 1141, 1176, 1207, 1239 and 1295 cm −1 are assigned to (i) Al–O symmetric stretch modes (3x) from the Al octahedra and (ii) the AlO 4 tetrahedron in the Al 13 unit and (iii) Al 3+ substituting Si 4+ in the Si 5O 16 unit. The low frequency Raman region is characterised by the symmetric bending modes of Si–O–Si at 202 cm −1 and Si–O–Al at 213 cm −1 in the Si 5O 16 unit. The third symmetric stretching mode at 271 cm −1 is assigned to Al–O–Al in the Al 13 unit. The five bands between 275 and 425 cm −1 are assigned to Si–O bending modes and the bands at 444 and 467 cm −1 to Al–O bending modes. The broad bands at 612 and 701 cm −1 are assigned to the Si–O–Al deformation modes, the latter of which is infrared inactive.

State-selected studies of the reaction of NH 3+ ( ν1, ν2) with D 2

The title reaction has been studied in a guided ion beam instrument at hyperthermal energies, resulting in ion products NH 3D + and NH 2D +. Ammonia ions were prepared with differing amounts of excitation in the in-plane symmetric stretching ( ν 1) and the out-of-plane symmetric bending mode ( ν 2) using 2+1 resonance-enhanced multiphoton ionization. Comparison of the reactivity of two nearly isoenergetic states ( ν 1=0, ν 2=5; internal energy, E int=0.60 eV and ν 1=1, ν 2=2; E int=0.63 eV) with differing concerted atom motions indicates that this reaction is not mode selective.

Vibrational relaxation of ClO2 in water

Photodissociation of ClO2 in aqueous solution at 400 nm results in the formation of ClO+O and Cl+O2. ClO and O geminately recombine to ClO2 in the electronic ground state (2B1), formed with an initial vibrational energy of ≈2.5 eV. In this paper the vibrational relaxation of ClO2(2B1) in aqueous solution is studied by femtosecond transient absorption spectroscopy in the spectral range 234 to 1024 nm. The measured transient absorption of the vibrationally relaxing ClO2 molecules is compared with the transient absorption calculated for relaxation in the asymmetric stretch as well as the symmetric stretch and bending modes. The calculations of the absorption spectra pertaining to the asymmetric stretch are based on a harmonic potential derived from the experimentally determined fundamental vibrational energy, whereas that of the symmetrical vibrations are based on ab initio potentials. An excellent agreement is obtained by assuming that the vibrational relaxation predominantly occurs in the asymmetric stretch with a 9.5 ps relaxation time. A weak spectral feature in the ultraviolet part of the spectrum is assigned to vibrational relaxation in the symmetric stretch and bending modes, indicating a coupling between the asymmetric and symmetric modes.

Observation of van der Waals vibrations in zero kinetic energy (ZEKE) photoelectron spectra of toluene-Ar van der Waals complex

Zero kinetic energy (ZEKE) photoelectron spectra due to van der Waals (vdW) vibrations have been observed for the toluene-Ar vdW complex in a supersonic free jet. ZEKE photoelectron measurements were carried out by using two-color (1 + 1′) resonant excitation followed by pulsed-field ionization (PFI). The first laser was tuned to the S 1 origin and its several specific vdW vibrational levels, while the second laser was scanned to observed a very low frequency vdW vibrational structure in the cation ground state ( D 0). From ZEKE photoelectron spectra thus obtained via several S 1 vdW vibrational levels, we have been able to identify the non-totally symmetric vdW bending mode ( b x +: 17 cm −1) and the vdW stretching mode ( s z +: 49 cm −1) for the toluene-Ar cation for the first time.

Intermolecular Coupling in Liquid and Crystalline States of trans-N-Methylacetamide Investigated by Polarized Raman and FT-IR Spectroscopies

The isotropic and anisotropic Raman spectra of neat N-methylacetamide (NMA) at different temperatures between −10 and 60 °C and NMA in acetonitrile were measured in order to spectroscopically compare and characterize the crystallized (T < 28 °C) and liquid states. These plus infrared data were subjected to a self-consistent component band analysis. We found that the amide I band is composed of two subbands in the solid phase and three in the liquid phase. For the former, the subbands at 1633 and 1656 cm-1 arise from transition dipole coupling interactions associated with the Ag and B2g species of the crystal unit cell. Depolarization ratio measurements suggest a departure from strict D2h symmetry. The three subbands in the liquid phase reflect different aggregate structures. The lowest frequency band at 1634 cm-1 results from an NMA oligomer exhibiting a structure similar to that observed in the ordered crystal phase. The most intense subband shows a significant negative noncoincidence effect, its isotropic component appearing at 1650 cm-1 and its anisotropic part at 1655 cm-1. This subband is interpreted as resulting from locally ordered short oligomeric hydrogen-bonded structures. The third subband is at 1675 cm-1 and results from isolated non-hydrogen-bonded NMA molecules or from amide I modes of the terminal groups of the above oligomers. Amide III shows a small but detectable positive noncoincidence effect in the liquid phase (2 cm-1), which is also assignable to transition dipole coupling between adjacent molecules in a locally ordered environment. The Raman bands arising from the symmetric bending modes of the two methyl groups are significantly affected by crystallization; the CCH3 symmetric bending mode becomes depolarized and less intense while the NCH3 symmetric bending mode gains intensity and becomes polarized. Ab initio calculations of torsional distortions of the CH3 groups, caused by interactions between adjacent non-hydrogen-bonded NMA molecules in the crystal, qualitatively reproduce these effects.