Raman and infrared spectral analysis of thallium niobyl phosphates: Tl2NbO2PO4, Tl3NaNb4O9(PO4)2 and TlNbOP2O7

Raman and infrared spectra of Tl2NbO2PO4, Tl3NaNb4O9(PO4)2 and TlNbOP2O7 are reported. The observed bands are assigned in terms of vibrations of NbO6 octahedra and PO4 tetrahedra in the first two compounds and in terms of NbO6 octahedra and P2O7 4− anion in the third compound. The NbO6 octahedra in all the title compounds are found to be corner-shared and distorted. The higher wavenumber values of the ν1 (NbO6) mode and other stretching modes indicate that the NbO6 octahedra in them are distorted in the order TlNbOP2O7 > Tl2NbO2PO4 > Tl3NaNb4O9(PO4)2. The splitting of the ν3 (PO4) mode indicates that PO4 tetrahedra is distorted more in Tl2NbO2PO4 than in Tl3NaNb4O9(PO4)2. The symmetry of P2O7 4− anion in TlNbOP2O7 is lowered. Bands indicate that the P–O–P bridge in the above compound has a bent P–O–P bridge configuration

Anharmonicity and local mode effects in the vibrational spectrum of NiCO4 and Co(CO)3NO

Previously published data on the vibrational fundamentals and overtones of the carbonyl stretching modes of Ni(CO)4 and Co(CO)3NO are reinterpreted using the recent model of Mills and Robiette, including Darling-Dennison resonances and local mode effects. The harmonic wavenumber θm and anharmonicity constant xm associated with the carbonyl and nitrosyl stretching modes are derived, and the 13C and 18O isotopic shifts are discussed in relation to the harmonic and anharmonic force field.

Chalcogenide-halides of niobium (V). 1. Gas-phase structures of NbOBr3, NbSBr3, and NbSCl3. 2. Matrix infrared spectra and vibrational force fields of NbOBr3, NbSBr3, NbSCl3, and NbOCl3

The molecular structures of NbOBr3, NbSCl3, and NbSBr3 have been determined by gas-phase electron diffraction (GED) at nozzle-tip temperatures of 250 degreesC, taking into account the possible presence of NbOCl3 as a contaminant in the NbSCl3 sample and NbOBr3 in the NbSBr3 sample. The experimental data are consistent with trigonal-pyramidal molecules having C-3v symmetry. Infrared spectra of molecules trapped in argon or nitrogen matrices were recorded and exhibit the characteristic fundamental stretching modes for C-3v species. Well resolved isotopic fine structure (Cl-35 and Cl-37) was observed for NbSCl3, and for NbOCl3 which occurred as an impurity in the NbSCl3 spectra. Quantum mechanical calculations of the structures and vibrational frequencies of the four YNbX3 molecules (Y = O, S; X = Cl, Br) were carried out at several levels of theory, most importantly B3LYP DFT with either the Stuttgart RSC ECP or Hay-Wadt (n + 1) ECP VDZ basis set for Nb and the 6-311 G* basis set for the nonmetal atoms. Theoretical values for the bond lengths are 0.01-0.04 Angstrom longer than the experimental ones of type r(a), in accord with general experience, but the bond angles with theoretical minus experimental differences of only 1.0-1.5degrees are notably accurate. Symmetrized force fields were also calculated. The experimental bond lengths (r(g)/Angstrom) and angles (angle(alpha)/deg) with estimated 2sigma uncertainties from GED are as follows. NbOBr3: r(Nb=O) = 1.694(7), r(Nb-Br) = 2.429(2), angle(O=Nb-Br) = 107.3(5), angle(Br-Nb-Br) = 111.5(5). NbSBr3: r(Nb=S) = 2.134(10), r(Nb-Br) = 2.408(4), angle(S=Nb-Br) = 106.6(7), angle(Br-Nb-Br) = 112.2(6). NbSCl3: Nb=S) = 2.120(10), r(Nb-Cl) = 2.271(6), angle(S=Nb-Cl) = 107.8(12), angle(Cl-Nb-Cl) = 111.1(11).

C-H...O hydrogen bonding in 4-phenyl-benzaldehyde: a comprehensive crystallographic, spectroscopic and computational study

The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O and C( 9)-H groups of adjacent molecules. In the liquid phase, the presence of C-(HO)-O-... bonded forms is revealed by both vibrational and NMR spectroscopy. A Delta H value of - 8.2 +/- 0.5 kJ mol(-1) for the dimerisation equilibrium is established from the temperature-dependent intensities of the bands assigned to the carbonyl-stretching modes. The NMR data suggest the preferential engagement of the C(2,6)-H and C(10/12)/C(11)-H groups as hydrogen bond donors, instead of the C(9)-H group. While ab initio calculations for the isolated dimers are unable to corroborate these NMR results, the radial distribution functions obtained from molecular dynamics simulations show a preference for C(2,6)-H and C(10/12)/C(11)-(HO)-O-... contacts relative to the C(9)-(HO)-O-... ones.

Solution behavior and surface properties of carboxymethylcellulose acetate butyrate

Solution behavior of carboxymethylcellulose acetate butyrate (CMCAB) in acetone and ethyl acetate has been investigated by small-angle X-ray scattering (SAXS) and capillary viscometry and correlated with the characteristics of CMCAB films. Viscosity and SAXS measurements showed that ethyl acetate is a better solvent than acetone for CMCAB. Thin films of CMCAB were deposited onto silicon wafers (Si/SiO(2)) by spin coating. AFM images revealed that CMCAB spin coated films from solutions prepared in ethyl acetate were homogeneous and flat. However, films obtained from solutions in acetone were very rough. Contact angle measurements with polar and apolar test liquids characterized CMCAB surfaces as hydrophobic and allowed estimating the surface energy of CMCAB. Sum frequency generation vibrational spectroscopy was used to understand the role played by solvents and to gain insight about molecular orientation at Si/SiO(2)/CMCAB interface.

Stability and interface properties of thin cellulose ester films adsorbed from acetone and ethyl acetate solutions

Stability and interface properties of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) films adsorbed from acetone or ethyl acetate onto Si wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Surface energy (gamma(total)(S)) values determined for CAP adsorbed from acetone are larger than those from ethyl acetate. In the case of CAB films adsorbed from ethyl acetate and acetone were similar. Dewetting was observed by AFM only for CAP films prepared from ethyl acetate. Positive values of effective Hamaker constant (A(eff)) were found only for CAP prepared from ethyl acetate, corroborating with dewetting phenomena observed by AFM. Oil the contrary, negative values of A(eff) were determined for CAP and CAB prepared from acetone and for CAB prepared from ethyl acetate, Corroborating with experimental observations. Sum frequency generation (SFG) vibrational spectra indicated that CAP and CAB films prepared from ethyl acetate present more alkyl groups oriented perpendicularly to the polymer-air interface than those films prepared from acetone. Such preferential orientation corroborates with macroscopic contact angle measurements. Moreover, SFG spectra showed that acetone hinds strongly to Si wafers, creating a new surface for CAP and CAB films. (C) 2008 Elsevier Inc. All rights reserved.

Structural Phase Transition Studies on PMN-0.35PT using Infrared Spectroscopy

The purpose of the present work is to report studies on structural phase transition for PMN-xPT ferroelectric, with melt PbTiO3 composition around the MPB (x = 0.35 mol %), using infrared spectroscopy technique. The study was centered on monitoring the behavior of the 1-(NbO), 1-(TiO) and 1-(MgO) stretching modes as a function of temperature. The increasing as a function of temperature for 1-(TiO) and 1-(MgO) modes, observed between 230 and 300 K, can be related to the monoclinic (MC) + tetragonal (T) phase coexistence in the PMN-PT.

Structural phase transitions of PbZr0.52Ti0.48O3 ceramic: An infrared spectroscopy study

The recent discovery of a ferroelectric monoclinic phase in the PbZr1-xTixO3 (PZT) system attained the attention of several researchers due to the possibility of understanding the relationships between structural features and piezoelectric properties. The nature of the monoclinic phase in some PZT compositions remains controversial and unclear. In this work, structural phase transitions of PbZr0.52Ti0.48O3 ceramic were investigated by infrared spectroscopy as a function of temperature. Studies were centered on nu(1)-stretching modes and corresponding half width Wi as a function of temperature. The occurrence of the anomalies in the infrared spectra as a function of temperature suggests the following monoclinic ( LT) -> monoclinic ( HT) -> tetragonal phase transition were observed at 183 K and at 263 K.

Infrared studies of the monoclinic-tetragonal phase transition in Pb(Zr, Ti)O-3 ceramics

Recently, the observation of a new monoclinic phase in the PbZr1-xTixO3 (PZT) system in the vicinity of the morphotropic phase boundary was reported. Investigations of this new phase were reported using different techniques such as high-resolution synchrotron x-ray powder diffraction and Raman spectroscopy. In this work, the monoclinic --> tetragonal phase transition in PbZr0.50Ti0.50O3 ceramics was studied using infrared spectroscopy between 1000 and 400 cm(-1). The four possible nu(1)-stretching modes (Ti-O and Zr-O stretch) in the BO6 octahedron in the ABO(3) structure of PZT in this region were monitored as a function of temperature. The lower-frequency mode nu(1)-(Zr-O) remains practically unaltered, while both intermediate nu(1)-(Ti-O) modes decrease linearly as temperature increases from 89 to 263 K. In contrast, the higher-frequency nu(1)-(Ti-O) and nu(1)-(Zr-O) modes present anomalous behaviour around 178 K. The singularity observed at this mode was associated with the monoclinic --> tetragonal phase transition in PbZr0.50Ti0.50O3 ceramics.

Structural Phase Transition Studies on PMN-0.35PT using Infrared Spectroscopy

The purpose of the present work is to report studies on structural phase transition for PMN-xPT ferroelectric, with melt PbTiO3 composition around the MPB (x = 0.35 mol %), using infrared spectroscopy technique. The study was centered on monitoring the behavior of the 1-(NbO), 1-(TiO) and 1-(MgO) stretching modes as a function of temperature. The increasing as a function of temperature for 1-(TiO) and 1-(MgO) modes, observed between 230 and 300 K, can be related to the monoclinic (MC) + tetragonal (T) phase coexistence in the PMN-PT.

Spectroscopic studies on glassy Ni(II) and Co(II) polyphosphate coacervates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigação espectroscópica dos carbonilos heterobimetálicos cis-[Fe(CO)4(HgX)2], X = Cl, Br,I

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Surface-enhanced resonance Raman scattering as an analytical tool for single molecule detection

A perylene derivative, n-(n-butyl)-n'-(4-aminobutyl) perylene-3,4,9,10-tetracarboxylic acid diimide (simplified as nBu-PTCD-(CH2)(4)-NH2) has been chosen as the target molecule for studies involving single molecule detection (SMD) using Raman scattering. The enhancement of the Raman signal is the result of the multiplicative effects of two phenomena, resonance Raman scattering (RRS) and surface-enhanced Raman scattering (SERS), which leads to the resulting surface-enhanced resonance Raman scattering (SERRS) process. The SERRS spectra from a single molecule have been collected using both silver and gold colloids. The SMD detection of the fundamental vibrational frequencies characteristic of nBu-PTCD-(CH2)(4)-NH2 is complemented with the detection of some overtones and combinations from ring stretching modes at the single molecule level. The background characterization of the ensemble vibrational spectroscopy of the target perylene and its SERRS is also presented, which includes the UV-vis absorption, experimental and calculated Raman scattering and infrared absorption, and molecular organization using reflection-absorption infrared spectroscopy (RAIRS).

Quantum mechanical modeling of excited electronic states and their relationship to cathodoluminescence of BaZrO3

First-principles calculations set the comprehension over performance of novel cathodoluminescence (CL) properties of BaZrO3 prepared through microwave-assisted hydrothermal. Ground (singlet, s*) and excited (singlet s** and triplet t**) electronic states were built from zirconium displacement of 0.2 Å in {001} direction. Each ground and excited states were characterized by the correlation of their corresponding geometry with electronic structures and Raman vibrational frequencies which were also identified experimentally. A kind of optical polarization switching was identified by the redistribution of 4dz2 and 4dxz (Zr) orbitals and 2pz O orbital. As a consequence, asymmetric bending and stretching modes theoretically obtained reveal a direct dependence with their polyhedral intracluster and/or extracluster ZrO6 distortions with electronic structure. Then, CL of the as-synthesized BaZrO3 can be interpreted as a result of stable triplet excited states, which are able to trap electrons, delaying the emission process due to spin multiplicity changes. © 2013 AIP Publishing LLC.

Estudos de materiais ferroelétricos por espectroscopia no infravermelho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)