Study of (9)Be+(12)C elastic scattering at energies near the Coulomb barrier

In this work, angular distribution measurements for the elastic channel were performed for the (9)Be + (12)C reaction at the energies E(Lab) = 13.0, 14.5, 17.3, 19.0 and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the framework of the double folding Sao Paulo potential. The experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies. However, for the three highest energies, an enhancement was observed for intermediate and backward angles. This can be explained by the elastic transfer mechanism. (C) 2011 Elsevier B.V. All rights reserved.

Elastic scattering of a proton-halo nucleus: (8)B+(58)Ni

The elastic channel of the (8)B + (58)Ni system has been measured at energies around the Coulomb barrier. An optical potential fi to the experimental angular distributions is obtained. The total reaction cross section consistent with the obtained potential is reported and possible deviations from normal behaviour are discussed.

Cooperative scattering by cold atoms

We have studied the interplay between disorder and cooperative scattering for the single scattering limit in the presence of a driving laser. Analytical results have been derived and we have observed cooperative scattering effects in a variety of experiments, ranging from thermal atoms in an optical dipole trap, atoms released from a dark MOT and atoms in a BEC, consistent with our theoretical predictions.

Two-Photon Polymerization for Fabricating Structures Containing the Biopolymer Chitosan

Two-photon polymerization is a powerful tool for fabricating three-dimensional micro/nano structures for applications ranging from nanophotonics to biology. To tailor such structure for specific purposes it is often important to dope them. In this paper we report on the fabrication of structures, with nanometric surface features (resolution of approximately 700 nm), using two-photon polymerization of an acrylic resin doped with the biocompatible polymer chitosan using a guest-host scheme. The fluorescence background in the Raman spectrum indicates the presence of chitosan throughout the structure. Mechanical characterization reveals that chitosan does not affect the mechanical properties of the host acrylic resin and, consequently, the structures exhibit excellent integrity. The approach presented in this work can be used in the fabrication of micro- and nanostructures containing biopolymers for biomedical applications.

Raman spectroscopy analysis of structural photoinduced changes in GeS(2) + Ga(2)O(3) thin films

Photoexpansion and photobleaching effects have been observed in amorphous GeS(2) + Ga(2)O(3) (GGSO) thin films, when their surfaces were exposed to UV light. The photoinduced changes on the surface of the samples are indications that the structure has been changed as a result of photoexcitation. In this paper, micro-Raman, energy dispersive X-ray analysis (EDX) and backscattering electrons (BSE) microscopy were the techniques used to identify the origin of these effects. Raman spectra revealed that these phenomena are a consequence of the Ge-S bonds` breakdown and the formation of new Ge-O bonds, with an increase of the modes associated with Ge-O-Ge bonds and mixed oxysulphide tetrahedral units (S-Ge-O). The chemical composition measured by EDX and BSE microscopy images indicated that the irradiated area is oxygen rich. So, the present paper provides fundamental insights into the influence of the oxygen within the glass matrix on the considered photoinduced effects. (C) 2010 Elsevier B.V. All rights reserved.

Modification of radiation pressure due to cooperative scattering of light

Cooperative spontaneous emission of a single photon from a cloud of N atoms modifies substantially the radiation pressure exerted by a far-detuned laser beam exciting the atoms. On one hand, the force induced by photon absorption depends on the collective decay rate of the excited atomic state. On the other hand, directional spontaneous emission counteracts the recoil induced by the absorption. We derive an analytical expression for the radiation pressure in steady-state. For a smooth extended atomic distribution we show that the radiation pressure depends on the atom number via cooperative scattering and that, for certain atom numbers, it can be suppressed or enhanced. Cooperative scattering of light by extended atomic clouds can become important in the presence of quasi-resonant light and could be addressed in many cold atoms experiments.

Detailed analysis of the charge transfer complex N,N-dimethylaniline-SO(2) by Raman spectroscopy and density functional theory calculations

Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N-dimethylaniline (DMA) and sulfur dioxide (SO(2)). The formation of a deep red oil by the reaction of SO(2) with DMA is an evidence of the charge transfer (CT) nature of the DMA-SO(2) interaction. The DMA -SO(2) normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm(-1), which are enhanced when resonance is approached. These bands are assigned to nu(s)(SO(2)) and nu(phi-N) vibrational modes, respectively, confirming the interaction between SO(2) and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO(2) with the ring pi electrons, which gives rise to a pi-pi* low-energy CT electronic transition, as confirmed by time-dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA-SO(2) spectrum at the B3LYP/6-311++g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb, detect, or even quantify SO(2). Copyright (C) 2009 John Wiley & Sons, Ltd.

Room Temperature Ionic Liquid-Lithium Salt Mixtures: Optical Kerr Effect Dynamical Measurements

The addition of lithium salts to ionic liquids causes an increase in viscosity and a decrease in ionic mobility that hinders their possible application as an alternative solvent in lithium ion batteries. Optically heterodyne-detected optical Kerr effect spectroscopy was used to study the change in dynamics, principally orientational relaxation, caused by the addition of lithium bis(trifluoromethylsulfonyl)imide to the ionic liquid 1-buty1-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Over the time scales studied (1 ps-16 ns) for the pure ionic liquid, two temperature-independent power laws were observed: the intermediate power law (1 ps to similar to 1 ns), followed by the von Schweidler power law. The von Schweidler power law is followed by the final complete exponential relaxation, which is highly sensitive to temperature. The lithium salt concentration, however, was found to affect both power laws, and a discontinuity could be found in the trend observed for the intermediate power law when the concentration (mole fraction) of lithium salt is close to chi(LiTf(2)N) = 0.2. A mode coupling theory (MCT) schematic model was also used to fit the data for both the pure ionic liquid and the different salt concentration mixtures. It was found that dynamics in both types of liquids are described very well by MCT.

Raman spectra of a pseudo-oxocarbon anion in ionic liquids

Raman and electronic spectra of the [3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate] dianion, the croconate violet (CV), are reported in solutions of ionic liquids based on imidazolium cations. Different normal modes of the CV anion, nu (C=O), nu (CO) + nu (CC) + nu (CCN), and nu(C N), were used as probes of solvation characteristics of ionic liquids, and were compared with spectra of CV in common solvents. The spectra of CV in ionic liquids are similar to those in dichloromethane solution, but distinct from those in protic solvents such as ethanol or water. The UV-vis spectra of CV in ionic liquids strongly suggest pi-pi interactions between the CV anion and the imidazolium cation. Copyright (C) 2009 John Wiley & Sons, Ltd.

Characterization of the products of aniline peroxydisulfate oligo/polymerization in media with different pH by resonance Raman spectroscopy at 413.1 and 1064 nm excitation wavelengths

The pH-structure correlation of the products of aniline peroxydisulfate reaction was mainly investigated by resonance Raman spectroscopy. The reactions of aniline and ammonium peroxydisulfate were carried out in aqueous solutions of initial pH ranging from 4.9 to 13.2 and monomer/oxidant molar ratio of 4/1. For an initial pH of 4.9, the spectroscopic techniques showed that the emeraldine salt form of polyaniline (PANI-ES) is the main product, corroborating that the usual head-to-tail coupling mechanism is taking place. The resonance Raman spectra at 1064 nm exciting wavelength were useful to detect the emeraldine salt as a minor product for reactions at an initial pH of 5.3-11.5. The Raman spectra of the main product of the reaction at initial pH of 13.2 excited at 1064 and 413.1 nm showed new spectral features consistent with 1,4-Michael-type adducts of aniline monomers and 1,4-benzoquinone-monoimine unit. These compounds and their products of hydrolysis/oxidation are the predominant species for the reaction media of initial pH from 5.3 to 13.2. In order to get PANI with different nanoscale morphologies, a pH value of more than 0 or 1 was used in the aniline polymerization. The spectroscopic data obtained in this work reveal that head-to-tail coupling does not occur when aniline reacts at media pH higher than about 5. It is suggested that chemical structures of the products of aniline oxidation by an unusual mechanism are the driving force for the development of assorted morphologies. Copyright (C) 2011 John Wiley & Sons, Ltd.

Unravelling the Chemical Morphology of a Mesoporous Titanium Dioxide Interface by Confocal Raman Microscopy: New Clues for Improving the Efficiency of Dye Solar Cells and Photocatalysts

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO(2), as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

The intramolecular charge transfer in a donor-pi-acceptor dianion probed by resonance Raman spectroscopy and quantum chemical calculations

The dideprotonation of 4-(4-nitrophenylazo)resorcinol generates an anionic species with substantial electronic pi delocalization. As compared to the parent neutral species, the anionic first excited electronic transition, characterized as an intramolecular charge transfer (ICT) from the CO(-) groups to the NO(2) moiety, shows a drastic red shift of ca. 200 nm in the lambda(max) in the UV-vis spectrum, leading to one of the lowest ICT energies observed (lambda(max) = 630 nm in dimethyl sulfoxide (DMSO)) in this class of push-pull molecular systems. Concomitantly, a threefold increase in the molar absorptivity (epsilon(max)) in comparison to the neutral species is observed. The resonance Raman enhancement profiles reveal that in the neutral species the chromophore involves several modes, as nu(C-N), nu(N=N), nu(C=C) and nu(s)(NO(2)), whereas in the dianion, there is a selective enhancement of the NO(2) vibrational modes. The quantum chemical calculations of the electronic transitions and vibrational wavenumbers led to a consistent analysis of the enhancement patterns observed in the resonance Raman spectra. Copyright (C) 2009 John Wiley & Sons, Ltd.

Raman spectroscopy of a sulfur dioxide visual sensor: The origin of the two colors in the solid sample

The vibrational spectroscopic characterization of a sulfur dioxide visual sensor was carried out using a Raman microscope system. It was observed the formation of two distinct complexes, that were characterized by the position and relative intensities of the bands assigned to the symmetric stretching, nu(s)(SO(2)),of the linked SO(2) molecules. In fact, in the yellowish orange complex, that corresponds to the 1:1 stoichiometry, only one band is observed, assigned to nu(s)(SO(2)) at ca. 1080 cm-(1) and, in the deep red complex, that corresponds to the 1:2 complex, at ca. 1070 and 1090 cm(-)1 are observed. The variation of the relative intensities of the bands assigned to nu(s)(SO(2)) present in the Ni(II)center dot SO(2) complex, in different points of the sample, shows clearly the requirement of the Raman microscope in the vibrational characterization of this kind of molecular sensor. (C) 2008 Elsevier B.V. All rights reserved.

Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))(3)](1-), L(-) = dopasemiquinone or L-dopasemiqui none, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the vCC + vCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g= 2.0005 and g = 2.0923, and for Cu(II) with g = 2.008 and g = 2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease. (c) 2008 Elsevier B.V. All rights reserved.

Structural and vibrational characterization of polyaniline nanofibers prepared from interfacial polymerization

This work deals with the structural and vibrational characterization of PANI nanofibers prepared through interfacial polymerization using different concentrations of HCl aqueous solution. The results were compared to those obtained by PANI prepared through the conventional route. X-ray diffraction and small-angle X-ray scattering techniques showed that high concentrations of HCl solutions used in the preparation of the PANI nanofibers reduce their crystallinity. The increase of regions with granular morphology was also observed in the scanning electron microscopy images. The changes in the resonance Raman spectra from 200 to 500 cm(-1), FTIR spectra, and the EPR data of the PANI nanofibers reveal an increase in the torsion angles of C-ring-N-C-ring segments owing the formation of bipolarons in the PANI backbone higher than the PANI samples prepared by conventional route.