Radiation induced phase separation in irradiated PTFE

The radiation induced phase separation in PTFE as shown by the observation of separation of its melting curves was investigated in this work. The observed phase separation was found to depend on irradiation temperature and explained as being duo to radiation induced increase in disorder of its crystalline region.     

Characterization of PVDF membranes by vibrational spectroscopy

In order to investigate the effectiveness of vibrational spectroscopy in the characterization of polymeric membranes, several poly(vinylidene fluoride) (PVDF) membranes with different porous structures were prepared by the phase inversion process using different casting solvents. An accurate analysis of the Fourier transform Raman (FT-Raman) and the Fourier transform infrared (FTIR) spectra was performed for each sample and the scanning electron microscopy (SEM) results were noted. To highlight the specific problems related to porosity and surface roughness in the acquisition of spectra by different sampling techniques, the attenuated total reflection (ATR) and photoacoustic spectroscopy (PAS) spectra were compared with corresponding spectra obtained from dense films. A detailed analysis of these spectra highlighted their ability in determining the differences in the polymer structure between the two membrane sides. This indicates that (considering the results given by all the different techniques) thorough qualitative membrane characterization can generally be achieved. Moreover, the good quality spectra of the PVDF membrane provide information on a portion of material which depends on its structure, highlighting the usefulness of FTIR-PAS in studying porous materials which, as a rule, give low quality infrared spectra when other sampling techniques are used. However, the complex and inhomogeneous structure of these materials can make quantitative analysis more, or less, difficult.     

Trihalogenomethane - base complexes studied by vibrational spectroscopy in low-temperature matrices

Hydrogen-bonded complexes formed by weak proton donors such as the trihalogenomethanes have received little attention. As a precursor to the study of such complexes, infrared and Raman spectra of trifluoromethane and trichloromethane were examined in argon, nitrogen and other matrices. The spectra of these trihalogenomethanes mixed with water or ammonia in argon or nitrogen matrices showed evidence of complex formation, the complexes with trichloromethane being stronger than those with trifluoromethane.     

Internal modes of iodopentamethylbenzene in the disordered phase by vibrational spectroscopy

Infrared and Raman spectra of oriented and non-oriented single crystal of iodopentamethylbenzene were measured at room temperature over the 4000-400 cm⁻¹ region. The dichroism of the IR bands is discussed. An assignment of the fundamental vibrations of IPMB is presented and based on a comparison with the spectra of some similar molecules.     

Characterization of parallel and antiparallel G-tetraplex structures by vibrational spectroscopy

A series of G-rich oligonucleotides able to form tetraplexes has been studied by FTIR spectroscopy. Characteristic markers of the formation of guanine tetrads are given. Moreover, we propose a new marker discriminating between parallel and antiparallel tetraplexes: the position of the C6O6 guanine carbonyl stretching vibration. In intermolecular parallel tetrameric structures formed by four separate strands this absorption is observed at 1693 cm-1 while for antiparallel tetrameric structures, either intramolecular or formed by dimerization of hairpins, this vibrational mode is observed at 1682 cm-1. These shifts to higher wavenumbers, when compared to the position of a free guanine C6O6 carbonyl stretching vibration observed at 1666 cm-1(Deltanu=27 cm-1 for parallel tetraplexes and Deltanu=16 cm-1 for antiparallel tetraplexes) reflect different strand orientations in the structures. This marker has been used to evidence the possibility of an antiparallel-parallel tetraplex reorganization for Oxytricha nova d(G4T4G4) and d((G4T4)3G4) and human d(G3T2AG3) telomeric sequences induced by Na+/K+ or Na+/Ca2+ ion exchange. Formation of the guanine tetrads, characterization of the phosphate geometries and of the sugar conformations have also been obtained by FTIR for the different tetraplexes.     

Thermodynamics of phase transitions in langmuir monolayers observed by vibrational sum frequency spectroscopy

Vibrational sum-frequency spectroscopy (VSFS) was used to study gauche defects in octadecylamine (ODA) monolayers at the air/water interface. The VSFS spectra provide unique insights into phase transitions that occur as a result of changes in the structure of the monolayer's hydrophobic region. These changes can be attributed to the increased presence of gauche conformers in the ODA alkyl chains during the monolayer's transition from the solid to liquid phase. Temperature-dependent spectra from monolayers at several different pressures were used to assign the phase transition temperature based on the observed changes in microscopic structure. Through application of a two-dimensional form of the Clapeyron equation, the first in situ measurements of the entropy and enthalpy changes associated with gauche conformers in a monolayer were made.     

Evidence for disorder in L-alanine lattice detected by Pulsed-EPR spectroscopy at cryogenic temperatures

The unusual behavior of lattice dynamics of L-alanine has been assigned to intermolecular dynamics and localization of vibrational energy. Recent heat capacity and Pulsed-EPR measurements support presence of thermally activated dynamic orientational disorder in the L-alanine lattice below 20 K. In the present study, the additional evidence for possible thermally activated disordered behavior of L-alanine lattice have been obtained by investigating dependences of longitudinal relaxation time of first stable L-alanine radical, SAR1, on sample cooling rates for the same low temperature interval. The obtained relaxation time by Pulsed-EPR shows clear dependence on cooling rates and this behavior can be explained within two types of suggested spin-lattice relaxation mechanisms for the paramagnetic centers in the hydrogen-bonded organic crystal.     

Gas phase vibrational spectroscopy of mass-selected vanadium oxide anions

The vibrational spectra of vanadium oxide anions ranging from V(2)O(6)(-) to V(8)O(20)(-) are studied in the region from 555 to 1670 cm(-1) by infrared multiple photon photodissociation (IRMPD) spectroscopy. The cluster structures are assigned and structural trends identified by comparison of the experimental IRMPD spectra with simulated linear IR absorption spectra derived from density functional calculations, aided by energy calculations at higher levels of theory. Overall, the IR absorption of the V(m)O(n)(-) clusters can be grouped in three spectral regions. The transitions of (i) superoxo, (ii) vanadyl and (iii) V-O-V and V-O single bond modes are found at approximately 1100 cm(-1), 1020 to 870 cm(-1), and 950 to 580 cm(-1), respectively. A structural transition from open structures, including at least one vanadium atom forming two vanadyl bonds, to caged structures, with only one vanadyl bond per vanadium atom, is observed in-between tri- and tetravanadium oxide anions. Both the closed shell (V(2)O(5))(2,3)VO(3)(-) and open shell (V(2)O(5))(2-4)(-) anions prefer cage-like structures. The (V(2)O(5))(3,4)(-) anions have symmetry-broken minimum energy structures (C(s)) connected by low-energy transition structures of C(2v) symmetry. These double well potentials for V-O-V modes lead to IR transitions substantially red-shifted from their harmonic values. For the oxygen rich clusters, the IRMPD spectra prove the presence of a superoxo group in V(2)O(7)(-), but the absence of the expected peroxo group in V(4)O(11)(-). For V(4)O(11)(-), use of a genetic algorithm was necessary for finding a non-intuitive energy minimum structure with sufficient agreement between experiment and theory.     

高灰煤中矿物质及碳结构的振动光谱分析

利用傅里叶变换红外光谱(FT-IR)、拉曼光谱和X射线衍射(XRD),分析了广西合山煤(GX)和平顶山煤(PD)及其酸洗煤的矿物质组分和碳结构。FT-IR谱图显示,GX和PD原煤的高岭石含量最为丰富,其次是石英和方解石,由二阶导数红外谱图发现,煤中还存在云母、蛇纹石、石膏和碱性长石。此外,从FT-IR谱图出现的三个层间水OH伸缩振动峰(3 695、3 651和3 619 cm^-1)判断煤中高岭石的结晶度不高。酸洗煤的FT-IR和XRD分别显示出清晰的芳香C=C官能团峰(1 600 cm^-1)和微晶碳(002)衍射峰;原煤的FT-IR和XRD都表明,矿物质完全掩盖了碳的信息。尽管如此,原煤及酸洗煤的拉曼谱图显示出清晰的缺陷碳峰(D峰)和石墨碳峰(G峰),而矿物质的信息完全被信号更强的碳峰掩盖。酸洗处理对煤的碳结构有较弱的影响,酸洗煤的碳结构有序度略低于原煤。     

Simultaneous measurement of magnitude and phase in interferometric sum-frequency vibrational spectroscopy

We present a visible-infrared sum-frequency spectroscopic technique that is capable of simultaneously determining the magnitude and phase of the sample response from a single set of experimental conditions. This is especially valuable in cases where the phase stability is high, as in collinear beam geometries, as it enables multiple experiments to be performed without re-measuring the local oscillator phase or the reference phase. After illustrating the phase stability achievable with such a geometry, we provide a technique for quantitatively determining the magnitude and phase from a single set of two-dimensional spectral-temporal interference fringes. A complete demonstration is provided for the C-H stretching frequency region at the surface of an octadecyltricholosilane film.     

Studies on the rubber phase stability in gamma irradiated polystyrene-SBR blends by using FT-IR and Raman spectroscopy

Improvement in the impact properties of polystyrene-SBR blends produced by different concentrations and types of styrene-butadiene rubber (SBR) was studied. The samples were gamma irradiated at different doses to achieve good adhesion, and consequently good stability, between the rubbery phase and the polystyrene matrix, producing an improvement in the impact properties. The results show that the best Izod impact was obtained for a blend with 10% SBR and with a dose of 100 kGy. Several samples with 0%, 3%, 5% and 10% of SBR were prepared and characterized by FT-IR and FT-Raman spectroscopies.     

Sol-gel phase transition of brucine-appended porphyrin gelator: a study by vibrational circular dichroism spectroscopy

A novel approach to study the sol-gel phase transition of a brucine–porphyrin based gelator, which uses vibrational circular dichroism (VCD) spectroscopy, is described. The gelation process leading to highly ordered chiral supramolecular assemblies was investigated in various solvents at the different temperatures and concentrations. The VCD spectra sensitively reveal the specific parts of molecule whose configuration is influenced by a sol-gel phase transition and chiral supramolecular aggregation and therefore indicate the parts of the molecule responsible for the chiral self-assembly formation. Temperature stability of the organogel studied is discussed on the basis of the VCD and IR absorption spectra. The scanning electron microscopy was used to visualize the structure of brucine–porphyrin conjugate in the gel phase.     

Structure of a gel phase lipid bilayer prepared by the Langmuir-Blodgett/Langmuir-Schaefer method characterized by sum-frequency vibrational spectroscopy

The structure of a planar supported lipid bilayer (PSLB) prepared by the Langmuir-Blodgett (LB)/Langmuir-Schaefer (LS) method was investigated by sum-frequency vibrational spectroscopy (SFVS). By using asymmetric lipid bilayers composed of selectively deuterated 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) lipids, the orientation of the fatty acid chains and phosphocholine headgroups has been determined independently for both leaflets of the bilayer. The alkyl chains of the lipids were found to be orientated approximately 13 degrees +/- 4 degrees from the surface normal for both leaflets. The lipid chains in both leaflets also contain some gauche content, which is consistent with previous NMR and FTIR studies of similar lipid systems. More importantly, the relative number of gauche defects does not seem to be influenced by the deposition method, LB versus LS. The headgroup orientation for the lipid film in contact with the silica support was determined to be 69 degrees +/- 3 degrees , whereas that in contact with the aqueous phase was 66 degrees +/- 4 degrees from the surface normal. The SFVS results indicate that the structure of the DSPC lipid film in contact with the solid support and the film adjacent to the aqueous phase are nearly identical in structure. These results suggesting the LB/LS deposition method do indeed produce symmetric lipid bilayers. These studies further add to the growing information on the efficacy of PSLBs as suitable models for biological membrane studies.     

Dispersion of the local parameters of quasilocalized low-frequency vibrational modes in a low-temperature glass: direct observation via single-molecule spectroscopy

Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6 < T < 40 K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses.     

Spin-dependent electron-phonon interaction in SmFeAsO by low-temperature Raman spectroscopy

The interplay between spin dynamics and lattice vibration has been suggested as an important part of the puzzle of high-temperature superconductivity. Here, we report the strong interaction between spin fluctuation and phonon in SmFeAsO, a parent compound of the iron arsenide family of superconductors, revealed by low-temperature Raman spectroscopy. Anomalous zone-boundary-phonon Raman scattering from spin superstructure was observed at temperatures below the antiferromagnetic ordering point, which offers compelling evidence on spin-dependent electron-phonon coupling in pnictides.     

Characterization of a synthetic peroxodiiron(III) protein model complex by nuclear resonance vibrational spectroscopy

The vibrational spectrum of an η(1),η(1)-1,2-peroxodiiron(III) complex was measured by nuclear resonance vibrational spectroscopy and fit using an empirical force field analysis. Isotopic (18)O(2) labelling studies revealed a feature involving motion of the {Fe(2)(O(2))}(4+) core that was not previously observed by resonance Raman spectroscopy.     

Pump-probe spectroscopy with phase-locked pulses in the condensed phase: decoherence and control of vibrational wavepackets

Electronic and vibrational coherences of Cl2 embedded in solid Ar are investigated by exciting to the B state with a phase-locked pulse pair from an unbalanced Michelson interferometer, where the chirp difference matches the B state anharmonicity. Recording the A' --> X fluorescence after relaxation is compared to probing to charge transfer states by a third pulse. The three-pulse experiment delivers more details on the decoherence processes. The signal modulation due to phase tuning up to the third vibrational round-trip time indicates that the electronic coherence in the B <-- X transition is preserved for more than 660 fs in the solid Ar environment where many body electronic interactions take place. Vibrational coherence lasts longer than 3 ps according to the observed half revival of the wavepacket. Control of the coupling between wavepacket motion and lattice oscillation is demonstrated by tuning the relative phase between the phase-locked pulses, preparing wavepackets predominantly composed of either zero-phonon lines or phonon side bands.     

Water-carbon dioxide mixtures at high temperatures and pressures: local order in the water rich phase investigated by vibrational spectroscopy

Raman scattering combined with near- and mid-infrared absorption spectroscopies was used to investigate the evolution of the local order in the water rich phase of water-CO(2) mixtures under isobaric heating (T=40-360 degrees C, P=250 bars). The quantitative analysis of the spectra shows that tetramers and larger oligomers are the main constituents of water at moderate temperatures below 80 degrees C. As the temperature increases, the dimer and trimer concentrations considerably increase at the expense of larger oligomers. Finally, water dimers are predominant at the highest temperature investigated close to the temperature of total miscibility of the mixture (T=366 degrees C, P=250 bars). This result is consistent with our previous investigation [R. Oparin T. Tassaing, Y. Danten, and M. Besnard, J. Chem. Phys. 120, 10691 (2004)] on water dissolved in the CO(2) rich phase where we found that close to the temperature of total miscibility water also exists mainly under dimeric form. The current study combined with that mentioned above provides a model investigation of the evolution of the state of aggregation of water molecules in binary mixture involving a hydrophobic solvent in a wide range of temperature.