Showing papers on "Infrared spectroscopy published in 1999"
TL;DR: The spontaneous Raman effect, in the following simply called Raman scattering, is focused on, which can be applied noninvasively under ambient conditions in almost every environment and has special importance for ultrasensitive Raman spectroscopy at the singlemolecule level.
Abstract: In the Raman effect, incident light is inelastically scattered from a sample and shifted in frequency by the energy of its characteristic molecular vibrations. Since its discovery in 1927, the effect has attracted attention from a basic research point of view as well as a powerful spectroscopic technique with many practical applications. The advent of laser light sources with monochromatic photons at high flux densities was a milestone in the history of Raman spectroscopy and resulted in dramatically improved scattering signals (for a general overview of modern Raman spectroscopy, see refs 1-5). In addition to this so-called spontaneous or incoherent Raman scattering, the development of lasers also opened the field of stimulated or coherent Raman spectroscopies, in which molecular vibrations are coherently excited. Whereas the intensity of spontaneous Raman scattering depends linearly on the number of probed molecules, the coherent Raman signal is proportional to the square of this number (for an overview, see refs 6 and 7). Coherent Raman techniques can provide interesting new opportunities such as vibrational imaging of biological samples,8 but they have not yet advanced the field of ultrasensitive trace detection. Therefore, in the following article, we shall focus on the spontaneous Raman effect, in the following simply called Raman scattering. Today, laser photons over a wide range of frequencies from the near-ultraviolet to the near-infrared region are used in Raman scattering studies, allowing selection of optimum excitation conditions for each sample. By choosing wavelengths which excite appropriate electronic transitions, resonance Raman studies of selected components of a sample or parts of a molecule can be performed.9 In the past few years, the range of excitation wavelengths has been extended to the near-infrared (NIR) region, in which background fluorescence is reduced and photoinduced degradation from the sample is diminished. High-intensity NIR diode lasers are easily available, making this region attractive for compact, low cost Raman instrumentation. Further, the development of low noise, high quantum efficiency multichannel detectors (chargecoupled device (CCD) arrays), combined with highthroughput single-stage spectrographs used in combination with holographic laser rejection filters, has led to high-sensitivity Raman spectrometers (for an overview on state-of-the-art NIR Raman systems, see ref 10). As we shall show in section 2, the nearinfrared region also has special importance for ultrasensitive Raman spectroscopy at the singlemolecule level. As with optical spectroscopy, the Raman effect can be applied noninvasively under ambient conditions in almost every environment. Measuring a Raman spectrum does not require special sample preparation techniques, in contrast with infrared absorption spectroscopy. Optical fiber probes for bringing excitation laser light to the sample and transporting scattered light to the spectrograph enable remote detection of Raman signals. Furthermore, the spatial and temporal resolution of Raman scattering are determined by the spot size and pulse length, respectively, of the excitation laser. By using a confocal microscope, Raman signals from femtoliter volumes (∼1 μm3) can by observed, enabling spatially resolved measurements in chromosomes and cells.11 Techniques such as multichannel Hadamard transform Raman microscopy12,13 or confocal scanning Fourier transform Raman microscopy14 allow generation of high-resolution Raman images of a sample. Recently, Raman spectroscopy was performed using near-field optical microscopy.15-17 Such techniques overcome the diffraction limit and allow volumes significantly smaller than the cube of the wavelength to be investigated. In the time domain, Raman spectra can be measured on the picosecond time scale, providing information on short-lived species such as excited 2957 Chem. Rev. 1999, 99, 2957−2975
2,057 citations
TL;DR: In this article, the authors demonstrate the use of the apertureless approach to scan near field optical microscopy to obtain contrast in vibrational absorption on a scale of about 100 nanometres, about one-hundredth of a wavelength.
Abstract: Identification of chemical compounds by vibrational spectroscopy at infrared wavelengths requires macroscopic samples: the spatial resolution is diffraction-limited to a scale of about half the wavelength, or about five micrometres. The scanning near-field optical microscope1,2, however, can reveal sub-wavelength detail because it uses near-field probing rather than beam focusing. Here we demonstrate the use of the aperture-less approach to scanning near-field optical microscopy3,4,5,6 to obtain contrast in vibrational absorption on a scale of about 100 nanometres, about one-hundredth of a wavelength. We record infrared scattering from the tip of an atomic force microscope scanned over a composite polymer film. At the boundary between different polymers we observe contrast changes owing to changes in vibrational absorption. The contrast is strongly enhanced in the near field of the probe tip, which we interpret as evidence of surface-enhanced infrared absorption7. When extended to multi-wavelength operation, this approach should enable imaging of chemical composition at nanometre resolution.
864 citations
TL;DR: In this article, the surface properties of high surface area ceria samples, either in the reduced or unreduced state, have been investigated using FT-IR spectroscopy.
755 citations
TL;DR: It was determined that in situ spectra of both schwertmannite and adsorbed sulfate are quite similar, suggesting that a continuum of outer- and inner-sphere sulfate occurs in both cases.
484 citations
TL;DR: In this paper, anhydrous mixtures of PolyBenzImidazole (PBI) with H 3 PO 4, H 2 SO 4 and HBr have been investigated by Infra Red spectroscopy and impedance measurements.
467 citations
TL;DR: In this paper, X-ray diffraction was used to determine the phase composition of manganese oxide catalysts, both bulk and supported on γ-Al2O3 and SiO2.
Abstract: Manganese oxide catalysts, both bulk and supported on γ-Al2O3 and SiO2, have been studied by Raman and FTIR spectroscopies, their phase composition being determined by X-ray diffraction. The supported catalysts were prepared via pore volume impregnation from nitrate precursors, the atomic ratio of manganese to aluminium and silicon, respectively, being in the range from 0.5/100 to 18/100. The use of Raman analysis in the microscopic configuration allowed the spectra to be taken at different points of the surface and revealed the inhomogeneity of the catalyst. Besides the Raman features of the β-MnO2 and α-Mn2O3 phases, other signals were assigned to isolated Mn2+ ions accommodated in tetrahedral vacancies on the support surface and to some epitaxial layers of γ-Mn2O3 and manganese silicate, respectively. The FTIR spectra, though not as useful because of the strong bands of the support that overlap those of manganese oxides, support these findings.
407 citations
TL;DR: The present review describes the applications of IR spectroscopy to the study of membrane proteins, with an emphasis on recent work and on spectra recorded in the transmission mode, rather than using reflectance techniques.
Abstract: Infrared (IR) spectroscopy is a useful technique in the study of protein conformation and dynamics. The possibilities of the technique become apparent specially when applied to large proteins in turbid suspensions, as is often the case with membrane proteins. The present review describes the applications of IR spectroscopy to the study of membrane proteins, with an emphasis on recent work and on spectra recorded in the transmission mode, rather than using reflectance techniques. Data treatment procedures are discussed, including band analysis and diAerence spectroscopy methods. A technique for the analysis of protein secondary and tertiary structures that combines band analysis by curve-fitting of original spectra with protein thermal denaturation is described in detail. The assignment of IR protein bands in H2O and in D2O, one of the more diAcult points in protein IR spectroscopy, is also reviewed, including some cases of unclear assignments such as loops, b-hairpins, or 310-helices. The review includes monographic studies of some membrane proteins whose structure and function have been analysed in detail by IR spectroscopy. Special emphasis has been made on the role of subunit III in cytochrome c oxidase structure, and the proton pathways across this molecule, on the topology and functional cycle of sarcoplasmic reticulum Ca 2+ -ATPase, and on the role of lipids in determining the structure of the nicotinic acetylcholine receptor. In addition, shorter descriptions of retinal proteins and references to other membrane proteins that have been studied less extensively are also included. # 1999 Elsevier Science Ltd. All rights reserved.
405 citations
TL;DR: In this paper, the effect of polymerization current density and monomer concentration on the formation of the film structure was studied with cyclic voltammetry, in situ UV-VIS-spectroelectrochemistry, electrochemical quartz crystal microbalance technique (EQCM), and in situ Fourier transform infrared (FTIR) spectroscopy using external and internal reflection techniques.
372 citations
TL;DR: In this paper, the adsorption of phosphate ions from aqueous solution onto thin films of colloidal TiO2 has been studied for the first time by in situ internal reflection infrared spectroscopy.
Abstract: The adsorption of phosphate ions from aqueous solution onto thin films of colloidal TiO2 has been studied for the first time by in situ internal reflection infrared spectroscopy. Phosphate binds strongly to TiO2, as evidenced by the large changes in the PO stretching band structure in the infrared spectrum of the adsorbed species compared with the solution species. The Langmuir binding constant for phosphate onto TiO2 at pH = 2.3 is (3.8 ± 0.8) × 104 dm3 mol-1, which is similar to the binding constants onto TiO2 for bidentate ligand species such as oxalate and catechol. The strength of the binding is also apparent in the kinetics of adsorption, showing fast adsorption and much slower desorption, as expected for a strongly bound species. The kinetics data at pH = 8.3 have indicated coverage-dependent phosphate adsorption and desorption. Experiments with substituted phosphate species have confirmed the bidentate binding of phosphate to Ti(IV) ions at the TiO2 surface.
369 citations
TL;DR: In this paper, carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand.
Abstract: Carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand. Five samples with diameters of 10.2, 10.8, 12.8, 19.4, and 33.6 A have been prepared as water-redispersible powders through decreasing the initial MSA/HAuCl4 molar ratio from 2.5 to 0.5. These samples were characterized by X-ray diffraction, transmission electron microscopy, elemental analysis, thermogravimetric analysis, ζ-potential measurement, Fourier transform infrared spectroscopy, and UV−vis spectroscopy. The results show that a large number of the particles are fcc single crystals with the polyhedral morphology of a truncated octahedral motif and that a self-assembled monolayer of thiolates has indeed formed through the adsorption of mercapto groups on the gold particle surface; the maximum packing density of the thiolates is 15.23 A2 per mercapto group. Th...
346 citations
TL;DR: A form of two-dimensional vibrational spectroscopy, which uses two ultrafast IR laser pulses, is used to examine the structure of a cyclic penta-peptide in solution and measures the coupling between the different amide groups in the structure.
Abstract: A form of two-dimensional (2D) vibrational spectroscopy, which uses two ultrafast IR laser pulses, is used to examine the structure of a cyclic penta-peptide in solution. Spectrally resolved cross peaks occur in the off-diagonal region of the 2D IR spectrum of the amide I region, analogous to those in 2D NMR spectroscopy. These cross peaks measure the coupling between the different amide groups in the structure. Their intensities and polarizations relate directly to the three-dimensional structure of the peptide. With the help of a model coupling Hamiltonian, supplemented by density functional calculations, the spectra of this penta-peptide can be regenerated from the known solution phase structure. This 2D-IR measurement, with an intrinsic time resolution of less than 1 ps, could be used in all time regimes of interest in biology.
TL;DR: In this article, the FT-IR and FT-Raman spectroscopy were used to characterize synthetic Mg-, Ni- and Co-hydrotalcite, and they showed that the composition changes brought about by changing the divalent metal result in small but significant changes in band positions of the modes related to the hydroxyl groups.
TL;DR: In situ infrared spectroscopy has been used to investigate the adsorption of a range of simple aromatic carboxylic acids from aqueous solution to metal oxides as discussed by the authors.
TL;DR: McCord et al. as discussed by the authors reported evidence of heavily hydrated salt minerals present over large areas of Europa's surface from analysis of reflectance spectra returned by the Galileo mission near infrared mapping spectrometer (NIMS).
Abstract: We reported evidence of heavily hydrated salt minerals present over large areas of Europa's surface from analysis of reflectance spectra returned by the Galileo mission near infrared mapping spectrometer (NIMS) [McCord et al., 1997a, b, 1998a, b]. Here we elaborate on this earlier evidence, present spatial distributions of these minerals, examine alternate water-ice interpretations, expand on our hydrated-salts interpretation, consider salt mineral stability on Europa, and discuss the implications. Extensive well-defined areas on Europa show distinct, asymmetric water-related absorption bands in the 1 to 2.5-μm region. Radiative transfer modeling of water ice involving different particle sizes and layers at Europa temperatures does not reproduce the distinctive Europa water bands. However, ice near its melting temperature, such as in terrestrial environments, does have some characteristics of the Europa spectrum. Alternatively, some classes of heavily hydrated minerals do exhibit such water bands. Among plausible materials, heavily hydrated salt minerals, such as magnesium and sodium sulfates, sodium carbonate and their mixtures, are preferred. All Europa spectral features are present in some salt minerals and a very good match to the Europa spectrum can be achieved by mixing several salt spectra. However, no single or mix of salt mineral spectra from the limited library available has so far been found to perfectly match the Europa spectrum in every detail. The material is concentrated at the lineaments and in chaotic terrain, which are technically disrupted areas on the trailing side. Since the spectrum of the material on Europa is nearly the same everywhere so-far studied, the salt or salt-mixture composition may be nearly uniform. This suggests similar sources and processes over at least a near-hemispheric scale. This would suggest that an extensive subsurface ocean containing dissolved salts is the source, and several possible mechanisms for deposit emplacement are considered. The hydrogen bonds associated with hydration of these salts are similar or greater in strength and energy to those in pure water ice. Thus, once on the surface, the salt minerals should be as stable to disruption as water ice at the Europa temperatures, and mechanisms are suggested to enhance the stability of both materials. Spectra obtained of MgSO4·6H2O at 77 K show only small differences from room temperature spectra. The main difference is the appearance of the individual absorptions composing the broad, composite water features and associated with the several different H2O sites in the salt hydrate molecule. This suggests that the Europa absorption bands are also composites. Thus higher spectral resolution may reveal these diagnostic features in Europa's spectrum. The specific salts present and their relative abundances would be indicators of the chemistry and conditions of an ocean environment, and areas of fresh, heavy concentration of these minerals should make ideal lander mission sampling sites.
TL;DR: In this paper, the interaction of self-assembled monolayers of 1,1′-biphenyl-4-thiol (BPT) with low energy electrons was explored.
Abstract: We have explored the interaction of self-assembled monolayers of 1,1′-biphenyl-4-thiol (BPT) with low energy electrons. X-ray photoelectron, infrared, and near edge x-ray absorption fine structure spectroscopy showed that BPT forms well-ordered monolayers with the phenyl rings tilted ∼15° from the surface normal. The films were exposed to 50 eV electrons and changes were monitored in situ. Even after high (∼10 mC/cm2) exposures, the molecules maintain their preferred orientation and remain bonded on the gold substrate. An increased etching resistance and changes in the infrared spectra imply a crosslinking between neighboring phenyl groups, which suggests that BPT can be utilized as an ultrathin negative resist. This is demonstrated by the generation of patterns in the underlying gold.
TL;DR: In this paper, the synthesis and characterization of alkyl-capped nanocrystalline Si (R-n−Si) prepared by the reaction of SiCl4 with Mg2Si in ethylene glycol dimethyl ether (glyme) and surface-terminated with various alkl groups was described.
Abstract: We describe the synthesis and characterization of alkyl-capped nanocrystalline Si (R-n−Si) prepared by the reaction of SiCl4 with Mg2Si in ethylene glycol dimethyl ether (glyme) and surface-terminated with various alkyl groups, R-n−Si (R = methyl, ethyl, n-butyl, and n-octyl). This reaction produces crystalline nanoparticles with surfaces that can be chemically modified. The resultant crystalline nanoparticles can be suspended in organic solvents or isolated as a powder. The nanoclusters were characterized by transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, UV−vis absorption, and photoluminescence spectroscopy. The average cluster size depends on the reflux time of Mg2Si with SiCl4, which provided nanoclusters with an average size of 2−5 nm. HRTEM confirms the presence of crystalline nanoclusters, and SAED is consistent with diamond-structured sil...
TL;DR: The use of the RDF code for the simulation of an infrared spectrum by a counterpropagation (CPG) neural network is shown and an empirical modelling process is used to refine this three-dimensional model of the molecular structure that corresponds to the infrared spectrum.
TL;DR: Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide, demonstrating that Europa's surface chemistry is dominated by radiolysis.
Abstract: Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis.
TL;DR: The atomic structure of icosahedral boron carbide was determined by comparing existing infrared absorption and Raman diffusion measurements with the predictions of accurate ab initio lattice-dynamical calculations performed for different structural models.
Abstract: The atomic structure of icosahedral ${\mathrm{B}}_{4}\mathrm{C}$ boron carbide is determined by comparing existing infrared absorption and Raman diffusion measurements with the predictions of accurate ab initio lattice-dynamical calculations performed for different structural models, a task presently beyond x-ray and neutron diffraction ability. By examining the inter- and intraicosahedral contributions to the stiffness we show that, contrary to recent conjectures, intraicosahedral bonds are harder.
TL;DR: In this paper, anion exchange reactions of layered Zn, Cu, Ni, or La hydroxide nitrates with the organic anions acetate, terephthalate, and benzoate are compared.
TL;DR: A number of iron−ZSM-5 catalysts have been prepared and characterized by X-ray absorption spectroscopy using fluorescence detection, electron spectrographs, temperature-programmed reduction, infrared spectrograms, and electron microscopy.
Abstract: A number of iron−ZSM-5 catalysts have been prepared and characterized by X-ray absorption spectroscopy using fluorescence detection, electron spectroscopy, temperature-programmed reduction, infrared spectroscopy, and electron microscopy. Iron has been introduced by aqueous exchange, by a novel method recently proposed by Feng and Hall (Catal. Lett. 1996, 41, 45), by exchange from a rigorously dried methanolic solution accompanied by agitation with ultrasound, and by a method intended to promote solid-state exchange. The degree of interaction with the zeolite framework has been probed by examining the effect on the zeolite proton OH band in the infrared spectrum. Less than 30% of the protons were exchanged from aqueous solution, but almost 80% exchange was achieved using ultrasound, as well as by the method reported by Feng and Hall (FH). Initially, both methods exhibited mainly isolated metal ions; however, calcination of the samples prepared according to FH exhibited rather large oxide clusters. After aq...
TL;DR: In this paper, an X-ray diffraction of the initial zinc sulfide−silica (ZSS) powder yields diffraction peaks corresponding to the ZnS phase.
Abstract: Ultrasonic irradiation of a slurry of amorphous silica microspheres, zinc acetate, and thioacetamide in an aqueous medium for 3 h under ambient air yields zinc sulfide coated on silica. The powder X-ray diffraction of the initial zinc sulfide−silica (ZSS) powder yields diffraction peaks corresponding to the ZnS phase. The TEM image of ZSS shows that the porous ZnS nanoparticles (diameter 1−5 nm) coated the silica (SiO2) surface as thin layers or nanoclusters, depending on the reactant concentration. Infrared spectroscopy illustrates the structural changes that occurred in the siloxane network and surface silanol groups of SiO2 upon the ultrasonic deposition of ZnS. The optical absorption of porous ZnS shows a broad band at around 610 nm, ascribed to unusual surface state transition. The absorption energy of the surface state transition is lower than the band gap of the ZnS particles and probably stems from the dangling surface bonds or defects. On the other hand, the ZSS does not show the surface state tr...
TL;DR: The spontaneous Raman effect has attracted attention from a basic research point of view as well as a powerful spectroscopic technique with many practical applications as discussed by the authors, however, it has not yet advanced the field of ultrasensitive trace detection.
Abstract: In the Raman effect, incident light is inelastically scattered from a sample and shifted in frequency by the energy of its characteristic molecular vibrations. Since its discovery in 1927, the effect has attracted attention from a basic research point of view as well as a powerful spectroscopic technique with many practical applications. The advent of laser light sources with monochromatic photons at high flux densities was a milestone in the history of Raman spectroscopy and resulted in dramatically improved scattering signals (for a general overview of modern Raman spectroscopy, see refs 1-5). In addition to this so-called spontaneous or incoherent Raman scattering, the development of lasers also opened the field of stimulated or coherent Raman spectroscopies, in which molecular vibrations are coherently excited. Whereas the intensity of spontaneous Raman scattering depends linearly on the number of probed molecules, the coherent Raman signal is proportional to the square of this number (for an overview, see refs 6 and 7). Coherent Raman techniques can provide interesting new opportunities such as vibrational imaging of biological samples,8 but they have not yet advanced the field of ultrasensitive trace detection. Therefore, in the following article, we shall focus on the spontaneous Raman effect, in the following simply called Raman scattering. Today, laser photons over a wide range of frequencies from the near-ultraviolet to the near-infrared region are used in Raman scattering studies, allowing selection of optimum excitation conditions for each sample. By choosing wavelengths which excite appropriate electronic transitions, resonance Raman studies of selected components of a sample or parts of a molecule can be performed.9 In the past few years, the range of excitation wavelengths has been extended to the near-infrared (NIR) region, in which background fluorescence is reduced and photoinduced degradation from the sample is diminished. High-intensity NIR diode lasers are easily available, making this region attractive for compact, low cost Raman instrumentation. Further, the development of low noise, high quantum efficiency multichannel detectors (chargecoupled device (CCD) arrays), combined with highthroughput single-stage spectrographs used in combination with holographic laser rejection filters, has led to high-sensitivity Raman spectrometers (for an overview on state-of-the-art NIR Raman systems, see ref 10). As we shall show in section 2, the nearinfrared region also has special importance for ultrasensitive Raman spectroscopy at the singlemolecule level. As with optical spectroscopy, the Raman effect can be applied noninvasively under ambient conditions in almost every environment. Measuring a Raman spectrum does not require special sample preparation techniques, in contrast with infrared absorption spectroscopy. Optical fiber probes for bringing excitation laser light to the sample and transporting scattered light to the spectrograph enable remote detection of Raman signals. Furthermore, the spatial and temporal resolution of Raman scattering are determined by the spot size and pulse length, respectively, of the excitation laser. By using a confocal microscope, Raman signals from femtoliter volumes (∼1 μm3) can by observed, enabling spatially resolved measurements in chromosomes and cells.11 Techniques such as multichannel Hadamard transform Raman microscopy12,13 or confocal scanning Fourier transform Raman microscopy14 allow generation of high-resolution Raman images of a sample. Recently, Raman spectroscopy was performed using near-field optical microscopy.15-17 Such techniques overcome the diffraction limit and allow volumes significantly smaller than the cube of the wavelength to be investigated. In the time domain, Raman spectra can be measured on the picosecond time scale, providing information on short-lived species such as excited 2957 Chem. Rev. 1999, 99, 2957−2975
TL;DR: In this paper, the Raman spectra of flame soot, collected in premixed flames at different flame heights and flame temperatures, were analyzed in regard to their structural properties and in comparison with those of disordered graphite.
Abstract: During combustion soot goes through different molecular structures. The Raman spectra of flame soot, collected in premixed flames at different flame heights and flame temperatures, were analysed in regard to their structural properties and in comparison with those of disordered graphite. Besides the G- and D-band of disordered graphite, a third Raman band at approximately 1188 cm-1 was observed which was tentatively assigned to mixed s–s bondings or to the C–C and C2C stretching vibration modes of polyene-like structures. The G-band position, the D-band width, and ID/IG intensity ratio describe the graphitic order in the particles. According to this result the graphitic order of the untreated soot particles decreases with decreasing flame temperature and flame height, whereas the size La of the graphitic sheets is nearly constant.
TL;DR: In this paper, the thermal stability of MCM-41 aluminosilicates is studied using 27 Al MAS NMR spectroscopy, and the tetrahedral to octahedral aluminium ratio is found to increase with higher aluminium incorporation.
IBM1
TL;DR: In this paper, the authors investigated the color stability of poly(9,9-dialkylfluorene-2,7-diyl) derivatives end-capped with 2-fluorenyl substituents.
Abstract: Poly(9,9-dialkylfluorene-2,7-diyl) derivatives end-capped with 2-fluorenyl, 9,9-di-n-hexyl-2-fluorenyl, and 9-fluorenone-2-yl substituents have been synthesized through Ni(0)-mediated polymerization. Absorption and emission spectra of these polymers were measured after annealing at elevated temperatures in air as a function of annealing time. The fluorescence stability of the polymers end-capped using 2-bromo-9,9-di-n-hexylfluorene was much better than for the polymers end-capped with 2-bromofluorene. The exceptional sensitivity of the luminescence of the polymers end-capped with 2-fluorenyl substituents to thermal annealing in air is rationalized by a combination of π-stacking and chemical oxidation of the end groups to fluorenones. The latter was demonstrated by the IR spectra of annealed films and comparison of the results with the absorption, emission, and IR spectra of the polymers deliberately end-capped using 2-bromo-9-fluorenone. This study is directed toward the investigation of color stability o...
TL;DR: In this paper, an innovative approach has been used to probe the molecular nature of the metal oxide/aqueous solution interface using internal reflection spectroscopy of thin colloidal TiO2 films, under aqueous solutions of pH 11.7−2.3.
Abstract: An innovative approach has been used to probe the molecular nature of the metal oxide/aqueous solution interface. Internal reflection spectroscopy of thin colloidal TiO2 films, under aqueous solutions of pH 11.7−2.3, has been used to obtain differential in situ infrared spectra related to interfacial species. An alkaline solution wash of the TiO2 films was shown to remove contaminants arising from the sol evaporation−film deposition process. Specific infrared absorptions have been assigned to terminal Ti−OH and Ti−OH2+, adsorbed water Ti−OH2, and bridging Ti−OH+−Ti species from the pH dependence of spectra and from deuteration experiments. These surface species determine the pH-dependent surface charge and the enhanced interfacial ionic concentrations observed in our previously published STIRS results. The enhanced interfacial ionic concentrations were also observed to have spectral effects related to interfacial water structure which are similar to those observed from concentrated aqueous solutions conta...
TL;DR: In this paper, the lattice vibrational modes of spinel-structured lithium manganese oxides have been calculated using atomistic modeling methods, and the results support a model for the Li 0.5Mn2O4 lattice in which the lithium ions are ordered.
Abstract: The lattice vibrational modes of spinel-structured lithium manganese oxides have been calculated using atomistic modeling methods. The simulations allow the Raman and infrared spectra of lithiated, fully delithiated, and partially delithiated phases to be assigned for the first time. Calculations for the spinels LiMn2O4, λ-MnO2, and Li0.5Mn2O4 are compared with experimental Raman data measured for thin films of the oxides coated on a platinum electrode. The appearance of a number of new bands in the Raman spectrum of LiMn2O4 following partial extraction of lithium is shown to result from local lowering of the symmetry and Raman activation of modes which are optically inactive or only infrared active in LiMn2O4. The results support a model for the Li0.5Mn2O4 lattice in which the lithium ions are ordered. The deformation vibrations of lattice hydroxyl “defects” in λ-MnO2 have also been calculated; comparison of the calculated and experimental vibrational data supports a model in which hydroxyl species are l...
TL;DR: In this article, the complete photocatalytic oxidation of C2H4 with O2 into CO2 and H2O has been achieved on ultrafine powdered TiO2 photocatalyst and the addition of H 2O was found to enhance the reaction.
TL;DR: In this paper, the authors review some literature studies about the characterisation of end groups in some fluoropolymers based on tetrafluoroethylene, vinylidene fluoride and vinyl fluoride.