Showing papers on "Infrared spectroscopy published in 2005"

Crystal modifications and thermal behavior of poly(L-lactic acid) revealed by infrared spectroscopy

Abstract: Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (PLLA) from the melt and glassy states, respectively [J. Phys. Chem. B 2004, 108, 11514; Macromolecules 2004, 37, 6433]. Surprisingly, the quite different infrared (IR) spectral evolutions occur in the two crystallization processes at different temperatures in which the same crystal modification is expected to be formed. To clarify this unusual phenomenon, the crystal modifications and thermal behavior of PLLA samples prepared under different crystallization temperatures are investigated in detail by TEM, WAXD, and FTIR techniques. On the basis of the WAXD and IR data, a new crystal modification named the α form is proposed for the crystal structure of PLLA samples annealed at temperature below 120 °C. Such crystal modification with loose 103 helical chain packing is less thermally stable than the standard α form of PLLA. This assignment can explain all the experiment observations well. Other possible mechanisms for the ...

Raman and IR spectroscopy of chemically processed single-walled carbon nanotubes.

Abstract: IR and Raman spectroscopy has been used to study the evolution of the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon present in arc-derived SWNT soot. We have carried out a systematic study to define the different outcomes stemming from the purification protocol (e.g., DO, DO/HCl, DO/HNO3, H2O2, H2O2/HCl), where dry oxidation (DO) or refluxing in H2O2 was used in a first purification step to remove amorphous carbon. The second step involves acid reflux (HCl or HNO3) to remove the residual growth catalyst (Ni−Y). During strong chemical processing, it appears possible to create additional defects where carbon atoms are eliminated, the ring structure is now open, localized CC bonds are created, and O-containing groups can be added to this defect to stabilize the structure. Evolution of SWNT skeletal disorder obtained via chemical processing was studied by Raman scattering. Higher intensity ratios of R...

Sequential proton transfer through water bridges in acid-base reactions.

Abstract: The proton transfer mechanism between aqueous Bronsted acids and bases, forming an encounter pair, has been studied in real time with ultrafast infrared spectroscopy. The transient intermediacy of a hydrated proton, formed by ultrafast dissociation from an optically triggered photoacid proton donor ROH, is implicated by the appearance of an infrared absorption marker band before protonation of the base, B-. Thus, proton exchange between an acid and a base in aqueous solution is shown to proceed by a sequential, von Grotthuss-type, proton-hopping mechanism through water bridges. The spectra suggest a hydronium cation H3O+ structure for the intermediate, stabilized in the Eigen configuration in the ionic complex RO-...H3O+...B-.

Signatures of the hydrogen bonding in the infrared bands of water.

Abstract: Infrared spectroscopy measurements have been completed over a wide range of frequencies allowing to measure the evolution of both intramolecular and intermolecular vibrational modes in water as a function of temperature. Emphasis is made on the high frequency OH stretching band and the so-called connectivity band that lies in the far infrared region. The substructures of the two infrared bands are analyzed in terms of different levels of connectivity of the water molecules, along the statements of the percolation model. Both band profiles appear to be related to the different degrees of connectivity of water molecules. Comparison of the data with the predictions of the percolation model shows good agreement as for the temperature evolution of liquid water. This work provides additional support to the interpretation of water bands substructures as signatures of its very specific connectivity pattern.

Functionalization of single-walled carbon nanotubes with well-defined polystyrene by "click" coupling.

Abstract: Covalent functionalization of alkyne-decorated SWNTs with well-defined, azide-terminated polystyrene polymers was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. This reaction was found to be extremely efficient in producing organosoluble polymer-nanotube conjugates, even at relatively low reaction temperatures (60 °C) and short reaction times (24 h). The reaction was found to be most effective when a CuI catalyst was employed in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive. IR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the SWNTs, and Raman spectroscopy evidenced the conversion of a high proportion of sp2 carbons to sp3 hybridization during alkyne introduction. Thermogravimetric analysis indicated that the polymer-functionalized SWNTs consisted of 45% polymer, amounting to approximately one polymer chain for every 200−700 carbons of the nanotubes, depending on polymer molecular weight. Transmission electron microscopy an...

Frequency-comb infrared spectrometer for rapid, remote chemical sensing

Abstract: We demonstrate real-time recording of chemical vapor fluctuations from 22m away with a fast Fourier-transform infrared (FTIR) spectrometer that uses a laser-like infrared probing beam generated from two 10-fs Ti:sapphire lasers. The FTIR’s broad 9–12μm spectrum in the “molecular fingerprint” region is dispersed by fast heterodyne self-scanning, enabling spectra at 2cm-1 resolution to be recorded in 70μs snapshots. We achieve continuous acquisition at a rate of 950 IR spectra per second by actively manipulating the repetition rate of one laser. Potential applications include video-rate chemical imaging and transient spectroscopy of e.g. gas plumes, flames and plasmas, and generally non-repetitive phenomena such as those found in protein folding dynamics and pulsed magnetic fields research.

C-H stretching vibrations of methyl, methylene and methine groups at the vapor/alcohol (N = 1-8) interfaces.

Abstract: In IR and Raman spectral studies, the congestion of the vibrational modes in the C-H stretching region between 2800 and 3000 cm(-1) has complicated spectral assignment, conformational analysis, and structural and dynamics studies, even with quite a few of the simplest molecules. To resolve these issues, polarized spectra measurement on a well aligned sample is generally required. Because the liquid interface is generally ordered and molecularly thin, and sum frequency generation vibrational spectroscopy (SFG-VS) is an intrinsically coherent polarization spectroscopy, SFG-VS can be used for discerning details in vibrational spectra of the interfacial molecules. Here we show that, from systematic molecular symmetry and SFG-VS polarization analysis, a set of polarization selection rules could be developed for explicit assignment of the SFG vibrational spectra of the C-H stretching modes. These polarization selection rules helped assignment of the SFG-VS spectra of vapor/alcohol (n = 1-8) interfaces with unprecedented details. Previous approach on assignment of these spectra relied on IR and Raman spectral assignment, and they were not able to give such detailed assignment of the SFG vibrational spectra. Sometimes inappropriate assignment was made, and consequently misleading conclusions on interfacial structure, conformation and even dynamics were reached. With these polarization rules in addition to knowledge from IR and Raman studies, new structural information and understanding of the molecular interactions at these interfaces were obtained, and some new spectral features for the C-H stretching modes were also identified. Generally speaking, these new features can be applied to IR and Raman spectroscopic studies in the condensed phase. Therefore, the advancement on vibrational spectra assignment may find broad applications in the related fields using IR and Raman as vibrational spectroscopic tools.

Spectroscopic characterization of the conformational states of the bis(trifluoromethanesulfonyl)imide anion (TFSI

Abstract: Ab initio calculations were combined with infrared and Raman studies to distinguish spectroscopically the two conformers of the bis(trifluoromethanesulfonyl)imide anion, (TFSI−). Spectra of crystalline LiTFSI complexes with organic ligands, where the anion adopts a known conformational state, are presented to confirm the calculated spectra. Several regions are identified where either the infrared or the Raman spectra contain separate bands for the two conformers. The conformational equilibrium between the transoid and cisoid rotamers is then illustrated from the infrared spectra of solutions of LiTFSI in aprotic solvents. The transoid form is found to be more stable than the cisoid form by about 2.2 kJ mol−1, in good agreement with the present and earlier theoretical predictions. It is also shown that the IR and Raman spectral changes coming from conformational isomerism have to be carefully distinguished from those due to ionic interactions. Copyright © 2005 John Wiley & Sons, Ltd.

Free electron laser-Fourier transform ion cyclotron resonance mass spectrometry facility for obtaining infrared multiphoton dissociation spectra of gaseous ions

Abstract: A Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been installed at a free electron laser (FEL) facility to obtain infrared absorption spectra of gas phase ions by infrared multiple photon dissociation (IRMPD). The FEL provides continuously tunable infrared radiation over a broad range of the infrared spectrum, and the FT-ICR mass spectrometer, utilizing a 4.7Tesla superconducting magnet, permits facile formation, isolation, trapping, and high-mass resolution detection of a wide range of ion classes. A description of the instrumentation and experimental parameters for these experiments is presented along with preliminary IRMPD spectra of the singly-charged chromium-bound dimer of diethyl ether (Cr(C4H10O)2+) and the fluorene molecular ion (C13H10+). Also presented is a brief comparison of the fluorene cation spectrum obtained by the FT-ICR-FEL with an earlier spectrum recorded using a quadrupole ion trap (QIT).

One-pot Synthesis of Polyaniline-metal Nanocomposites

Abstract: Composite materials consisting of polyaniline nanofibers decorated with noble-metal (Ag or Au) nanoparticles were synthesized with γ radiolysis. Aqueous solutions of aniline, a free-radical oxidant, and/or a metal salt were irradiated with γ rays. Exposure of the solutions to γ rays caused aniline to polymerize as very-thin fibers. Metal particles were also formed during irradiation and decorated the fibers. The shape and size of the metal particles could be changed from nanometer-sized spheres to micron-sized dendrites by varying the ratio of aniline to the metal precursor. Polyaniline-metal composites were characterized using UV−Vis spectroscopy, infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The electrical conductivity of the composites increased with the loading of metal in the nanocomposites and was up to 50 times greater than that of polyaniline fibers alone.

The composition and structure of Pd-Au surfaces

Abstract: Pd, Au, and Pd-Au mixtures were deposited via physical vapor deposition onto a Mo(110) substrate, and the surface concentration and morphology of the Pd-Au mixtures were determined by low-energy ion scattering spectroscopy (LEISS), infrared absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Pd-Au mixtures form a stable alloy between 700 and 1000 K with substantial enrichment in Au compared to the bulk composition. Annealing a 1:1 Pd-Au mixture at 800 K leads to the formation of a surface alloy with a composition Au(0.8)Pd(0.2) where Pd is predominantly surrounded by Au. The surface concentration of this isolated Pd site can be systematically controlled by altering the bulk Pd-Au alloy concentration.

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts.

Abstract: Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1–7.3wt%). Collectively, this series of catalysts provides a range of metal particle sizes (1.2–8.5nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)∕(111) and (111)∕(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1wt% loaded catalysts, with the relative inactivity of the cataly...

Lithium Ethylene Dicarbonate Identified as the Primary Product of Chemical and Electrochemical Reduction of EC in 1.2 M LiPF6/EC:EMC Electrolyte

Abstract: Lithium ethylene dicarbonate ((CH2OCO2Li)2) was chemically synthesized and its Fourier transform infrared (FTIR) spectrum was obtained and compared with that of surface films formed on Ni after cyclic voltammetry (CV) in 1.2 M lithium hexafluorophosphate (LiPF6)/ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7, w/w) electrolyte and on metallic lithium cleaved in-situ in the same electrolyte. By comparison of IR experimental spectra with that of the synthesized compound, we established that the title compound is the predominant surface species in both instances. Detailed analysis of the IR spectrum utilizing quantum chemical (Hartree-Fock) calculations indicates that intermolecular association through O...Li...O interactions is very important in this compound. It is likely that the title compound in the passivation layer has a highly associated structure, but the exact intermolecular conformation could not be established on the basis of analysis of the IR spectrum.

The effect of cooperative hydrogen bonding on the OH stretching-band shift for water clusters studied by matrix-isolation infrared spectroscopy and density functional theory.

Abstract: Infrared spectra of the water clusters have been measured in the N2 + O2 matrix. The aggregation process of water in the matrix has been monitored by annealing the deposited samples up to 40 K and UV irradiation. The monomer, dimer, cyclic trimer and cyclic pentamer are found as water clusters in the matrix. For the hexamer, several structures such as chair, cage, prism, bag 1 and/or book 1 are likely to exist. By UV irradiation, the cyclic pentamer is predominantly formed from the monomer and dimer. On the other hand, by annealing the deposited sample, several hexamers are formed. The theoretical calculation for water clusters has revealed that the formation of one hydrogen bonding in a hydrogen-bonded chain cooperatively enhances or diminishes the strength of another hydrogen bond. Both proton donor (D) and acceptor (A) participating in a hydrogen-bonding pair DA are capable of forming hydrogen bonding with the other water molecules; D can additionally accept two protons and donate one proton, and A can additionally donate two protons and accept one proton. We have proposed the classification of hydrogen-bonding patterns considering the cooperativity, denoting as d′a′DAd″a″, where d and a are integers indicating the number of proton donors and acceptors to D (the single prime) and A (the double prime), respectively. Then, a magnitude given by MOH = −d′ + a′ + d″ − a″ has been introduced, which is very useful for connecting the hydrogen-bonding patterns to their OH wavenumbers. As a result, it is revealed that the OH stretching bands of water clusters are characterized by eight indicators (free and MOH = −2, −1, 0, 1, 2, 3 and 4). The classification proposed here is applicable to the OH band analysis for the hydrogen-bonded water and alcohols in a condensed phase.

Carbon dioxide capture by diamine-grafted SBA-15: A combined Fourier transform infrared and mass spectrometry study

Abstract: The adsorption and desorption of CO2 on diamine-grafted SBA-15 have been studied by infrared spectroscopy coupled with mass spectrometry. Diamine was grafted onto the SBA-15 surface by the reaction of [N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane with the surface OH. CO2 is adsorbed on the diamine-grafted SBA-15 as bidentate carbonate and bidentate and monodentate bicarbonates at 25 °C. Bidentate carbonate and monodentate bicarbonates are the major surface species formed and decomposed during the concentration-swing adsorption/desorption process at 25 °C. Temperature-programmed desorption revealed that the monodentate and bidentate bicarbonates bound stronger to the diamine-grafted SBA-15 surface than the bidentate carbonate. The amount of CO2 desorbed from the carbonate and bicarbonate between 30 and 120 °C is 2 times more than that of CO2 adsorbed/desorbed during each cycle of the concentration-swing adsorption/desorption. Desorption at 120 °C removes the majority of the captured CO2 and regenerates ...

High-resolution absorption cross-section of glyoxal in the UV–vis and IR spectral ranges

Abstract: High-resolution absorption cross-sections of glyoxal have been recorded at 296 K in the ultraviolet and visible (UV–vis: 19000–40000 cm−1, 250–526 nm) and infrared (IR: 1200–8000 cm−1) spectral ranges by means of a Fourier transform spectrometer (FTS). The UV–vis spectra were measured at 1 atm of N2 bath gas. The spectral resolution of the FTS was selected to be 0.06 cm−1 for the richly structured A ˜ 1Au – X ˜ 1Ag and a ˜ 3Au – X ˜ 1Ag band systems, and 1 cm−1 for the diffuse B ˜ − X ˜ transition, which was sufficient to resolve most spectral structures. In addition, low and high-resolution IR spectra (1 and 0.009 cm−1 spectral resolution) of glyoxal/N2 mixtures were recorded around 2835 cm−1 at 0.2 mbar, 100 mbar, 300 mbar and 1 atm total pressure. UV–vis and IR spectra were recorded quasi-simultaneously by making sequential measurements of identical glyoxal mixtures in the cell, enabling the direct comparison of UV–vis and IR spectral parameters for the first time. The high-resolution spectra have been used to simulate deviations from Lambert–Beer's law, which occur at lower resolution when spectra are not fully resolved. Special attention has been paid to reduce the uncertainty of the UV–vis spectrum, allowing for an improved determination of the atmospheric photolysis of glyoxal. Finally, the new UV–vis spectrum has been used to redetermine our previous DOAS measurements of glyoxal yields from the reactions of OH radicals with benzene, toluene and p-xylene. The high-resolution spectral data can be obtained from http://iup.physik.uni-bremen.de/gruppen/molspec/index.html or email request to the authors.

Covalently attached monolayers on crystalline hydrogen-terminated silicon: extremely mild attachment by visible light.

Abstract: A very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. By using visible light sources, from 447 to 658 nm, a variety of 1-alkenes and 1-alkynes were attached to hydrogen-terminated Si(100) and Si(111) surfaces at room temperature. The presence and the quality of the monolayers were evaluated by static water contact angles, X-ray photoelectron spectroscopy, and IR spectroscopy. Monolayers prepared by thermal, UV light, or visible light initiation were compared. Additionally, the ability of infrared reflection−absorption spectroscopy to study organic monolayers on silicon was explored. A reaction mechanism is discussed on the basis of investigations of the reaction behavior of 1-alkenes with silicon wafers with varying types and levels of doping. Finally, a series of mixed monolayers derived from the mixed solutions of a 1-alkene and an ω-fluoro-1-alkene were investigated to reveal that the composition of the mixed monolayers was directly prop...

White-light emission of polyvinyl alcohol/ZnO hybrid nanofibers prepared by electrospinning

Abstract: Polyvinyl alcohol∕ZnO (PVA∕ZnO) hybrid nanofibers were prepared by the electrospinning technique. The structural and spectral information of the nanofibers was characterized by scanning electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, resonant Raman, and photoluminescence (PL). The results indicate that ZnO were successfully embedded in the one-dimensional hybrid fibers via chemical interactions between ZnO and PVA. PL results show the PVA∕ZnO nanofibers have an intense white-light emission, which originates from the simultaneous emission of three bands covering from the UV to visible range. A possible PL mechanism was proposed accordingly.

Surface passivation of bare aluminum nanoparticles using perfluoroalkyl carboxylic acids

Abstract: Surface passivation of unpassivated Al nanoparticles has been realized using self-assembled monolayers (SAMs). Nanoscale Al particles were prepared in solution by catalytic decomposition of H 3 Al.NMe 3 or H 3 Al.N(Me)Pyr by Ti(O i Pr) 4 and coated in situ using a perfluoroalkyl carboxylic acid SAM. Because the Al particles are prepared using wet chemistry techniques and coated in solution, they are free of oxygen passivation. This SAM coating passivates the aluminum and appears to prevent the oxidation of the particles in air and renders the composite material, to some extent, soluble in polar organic solvents such as diethyl ether. Characterization data including scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and attenuated total reflectance-Fourier transform infrared spectroscopy of prepared materials are presented.

Effect of chemical treatment on electrical conductivity, infrared absorption, and Raman spectra of single-walled carbon nanotubes.

Abstract: We investigate the magnitude and temperature dependence of electrical conductivity, the optical and infrared absorption, and the Raman spectra of single-walled carbon nanotube (SWNT) bucky-paper after chemical treatment and determine the correlations between the changes in these properties. Ionic-acceptor doping of the SWNT bucky-paper (with SOCl(2), iodine, H(2)SO(3), etc.) causes an increase of electrical conductivity that correlates with an increase of the absorbance in the far-IR region and an increase in the frequency of Raman spectral lines. Conversely, treatment with other molecules (e.g., aniline, PyPhF(5), PhCH(2)Br, etc.) leads to a decrease in both conductivity and far-IR absorption. The temperature dependence of the conductivity gives a good indication of the presence of metallic charge carriers and is in agreement with the model of interrupted metallic conduction.

Atomic Structure of a Thin Silica Film on a Mo(112) Substrate: A Two-Dimensional Network of SiO4 Tetrahedra

Abstract: The structure of a thin single crystalline SiO2 film grown on Mo(112) has been studied by scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. In excellent agreement with the experimental results, density functional theory calculations show that the film consists of a two-dimensional network of corner sharing [SiO4] tetrahedra, with one oxygen of each tetrahedron binding to the protruding Mo atoms of the Mo(112) surface.

FTIR studies of the effects of pigments on the aging of oil

Abstract: Describes the changes in the infrared spectra of oil paint as a result of ageing. The focus is on the influence of pigments on the long term changes in the oil binding medium. Several naturally aged paints made with different pigments were analysed using Fourier-transform infrared spectroscopy (FTIR). One of the most pronounced effects observed in the infrared spectra of ageing paint is the shifting and broadening of the carbonyl band due to the formation of carboxylic acids. Another effect of pigments on the oil binding medium is the catalysis of the hydrolysis of triglycerides, as indicated by the increasing intensity of the ester absorption. Finally, the nature of the pigments included has a profound effect on the CH strength absorptions. From these results it is clear that pigments can significantly alter the infrared spectra of drying oil, and should therefore be identified to ensure correct assessment of the infrared spectra in the drying paint.