Showing papers on "Infrared spectroscopy published in 2004"
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30 Jul 2004
TL;DR: In this paper, the authors present a set of techniques for detecting anomalous infrared spectra, including Fourier Transform Infrared Spectrometers (FTIS) and Spectral Spectral Transform Transform (STT) this paper.
Abstract: Series Preface.Preface.Acronyms, Abbreviations and Symbols.About the Author.1. Introduction.1.1 Electromagnetic Radiation.1.2 Infrared Absorptions.1.3 Normal Modes of Vibration.1.4 Complicating Factors.1.4.1 Overtone and Combination Bands.1.4.2 Fermi Resonance.1.4.3 Coupling.1.4.4 Vibration-Rotation Bands.References.2. Experimental Methods.2.1 Introduction.2.2 Dispersive Infrared Spectrometers.2.3 Fourier-Transform Infrared Spectrometers.2.3.1 Michelson Interferometers.2.3.2 Sources and Detectors.2.3.3 Fourier-Transformation.2.3.4 Moving Mirrors.2.3.5 Signal-Averaging.2.3.6 Advantages.2.3.7 Computers.2.3.8 Spectra.2.4 Transmission Methods.2.4.1 Liquids and Solutions.2.4.2 Solids.2.4.3 Gases.2.4.4 Pathlength Calibration.2.5 Reflectance Methods.2.5.1 Attenuated Total Reflectance Spectroscopy.2.5.2 Specular Reflectance Spectroscopy.2.5.3 Diffuse Reflectance Spectroscopy.2.5.4 Photoacoustic Spectroscopy.2.6 Microsampling Methods.2.7 Chromatography-Infrared Spectroscopy.2.8 Thermal Analysis-Infrared Spectroscopy.2.9 Other Techniques.References.3. Spectral Analysis.3.1 Introduction.3.2 Group Frequencies.3.2.1 Mid-Infrared Region.3.2.2 Near-Infrared Region.3.2.3 Far-Infrared Region.3.3 Identification.3.4 Hydrogen Bonding.3.5 Spectrum Manipulation.3.5.1 Baseline Correction.3.5.2 Smoothing.3.5.3 Difference Spectra.3.5.4 Derivatives.3.5.5 Deconvolution.3.5.6 Curve-Fitting.3.6 Concentration.3.7 Simple Quantitative Analysis.3.7.1 Analysis of Liquid Samples.3.7.2 Analysis of Solid Samples.3.8 Multi-Component Analysis.3.9 Calibration Methods.References.4. Organic Molecules.4.1 Introduction.4.2 Aliphatic Hydrocarbons.4.3 Aromatic Compounds.4.4 Oxygen-Containing Compounds.4.4.1 Alcohols and Phenols.4.4.2 Ethers.4.4.3 Aldehydes and Ketones.4.4.4 Esters.4.4.5 Carboxylic Acids and Anhydrides.4.5 Nitrogen-Containing Compounds.4.5.1 Amines.4.5.2 Amides.4.6 Halogen-Containing Compounds.4.7 Heterocyclic Compounds.4.8 Boron Compounds.4.9 Silicon Compounds.4.10 Phosphorus Compounds.4.11 Sulfur Compounds.4.12 Near-Infrared Spectra.4.13 Identification.References.5. Inorganic Molecules.5.1 Introduction.5.2 General Considerations.5.3 Normal Modes of Vibration.5.4 Coordination Compounds.5.5 Isomerism.5.6 Metal Carbonyls.5.7 Organometallic Compounds.5.8 Minerals.References.6. Polymers.6.1 Introduction.6.2 Identification.6.3 Polymerization.6.4 Structure.6.5 Surfaces.6.6 Degradation.References.7. Biological Applications.7.1 Introduction.7.2 Lipids.7.3 Proteins and Peptides.7.4 Nucleic Acids.7.5 Disease Diagnosis.7.6 Microbial Cells.7.7 Plants.7.8 Clinical Chemistry.References.8. Industrial and Environmental Applications.8.1 Introduction.8.2 Pharmaceutical Applications.8.3 Food Science.8.4 Agricultural Applications.8.5 Pulp and Paper Industries.8.6 Paint Industry.8.7 Environmental Applications.References.Responses to Self-Assessment Questions.Bibliography.Glossary of Terms.SI Units and Physical Constants.Periodic Table.Index.
2,802 citations
TL;DR: A novel type of Fourier-transform infrared spectrometer based on two Ti:sapphire lasers emitting femtosecond pulse trains with slightly different repetition frequencies that superimposed upon a detector to produce purely time-domain interferograms that encode the infrared spectrum is demonstrated.
Abstract: A novel type of Fourier-transform infrared spectrometer (FTIR) is demonstrated. It is based on two Ti:sapphire lasers emitting femtosecond pulse trains with slightly different repetition frequencies. Two mid-infrared beams-derived from those lasers by rectification in GaSe-are superimposed upon a detector to produce purely time-domain interferograms that encode the infrared spectrum. The advantages of this spectrometer compared with the common FTIR include ease of operation (no moving parts), speed of acquisition (100 micros demonstrated), and not-yet-shown collimated long-distance propagation, diffraction-limited microscopic probing, and electronically controllable chemometric factoring. Extending time-domain frequency-comb spectroscopy to lower (terahertz) or higher (visible, ultraviolet) frequencies should be feasible.
697 citations
TL;DR: A simple one-step hydrothermal reaction among TiO2 powders and alkaline solution has been developed to synthesize low-dimensional titanate nanostructures.
492 citations
TL;DR: Size-dependent development of the hydrogen bond network structure in largesized clusters of protonated water, H+(H2O)n, was probed by infrared spectroscopy of OH stretches by demonstrating that the chain structures at small sizes develop into two-dimensional net structures and then into nanometer-scaled cages.
Abstract: Size-dependent development of the hydrogen bond network structure in largesized clusters of protonated water, H+(H2O)n (n = 4 to 27), was probed by infrared spectroscopy of OH stretches. Spectral changes with cluster size demonstrate that the chain structures at small sizes (n ≲ 10) develop into two-dimensional net structures (∼10
489 citations
TL;DR: In this paper, the effects of halide anions on the water structure of the bulk solution to that of the interface were examined using vibrational sum frequency generation spectroscopy.
Abstract: Air−aqueous sodium halide solution interfaces are examined using vibrational sum frequency generation spectroscopy. Raman and ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopies are also used to compare the effects of halide anions on the water structure of the bulk solution to that of the interface. The interfacial water structures for the sodium fluoride and chloride aqueous solutions are found to be similar to the air−water interface, whereas sodium bromide and iodide aqueous solutions cause significant distortion of the hydrogen-bonding network. Analysis of the spectra indicates higher concentrations of bromide and iodide anions in the interfacial region with an increase in interfacial depth.
457 citations
TL;DR: In this article, the authors examined the surface functional group chemistry of intact Gram-positive and Gram-negative bacterial cells and their isolated cell walls using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.
Abstract: Surface functional group chemistry of intact Gram-positive and Gram-negative bacterial cells and their isolated cell walls was examined as a function of pH, growth phase, and growth media (for intact cells only) using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy Infrared spectra of aqueous model organic molecules, representatives of the common functional groups found in bacterial cell walls (ie, hydroxyl, carboxyl, phosphoryl, and amide groups), were also examined in order to assist the interpretation of the infrared spectra of bacterial samples The surface sensitivity of the ATR-FTIR spectroscopic technique was evaluated using diatom cells, which possess a several-nanometers-thick layer of glycoprotein on their silica shells The ATR-FTIR spectra of bacterial surfaces exhibit carboxyl, amide, phosphate, and carbohydrate related features, and these are identical for both Gram-positive and Gram-negative cells These results provide direct evidence to the previously held conviction that the negative charge of bacterial surfaces is derived from the deprotonation of both carboxylates and phosphates Variation in solution pH has only a minor effect on the secondary structure of the cell wall proteins The cell surface functional group chemistry is altered neither by the growth phase nor by the growth medium of bacteria This study reveals the universality of the functional group chemistry of bacterial cell surfaces
433 citations
TL;DR: In this paper, the attenuated total reflection−infrared (ATR−IR) spectra in the 4800−700 cm-1 range of nine carboxylic acids and their sodium salts in aqueous solutions are obtained and analyzed.
Abstract: The attenuated total reflection−infrared (ATR−IR) spectra in the 4800−700 cm-1 range of nine carboxylic acids and their sodium salts in aqueous solutions are obtained and analyzed. Overall, 22 species are studied. Six IR titrations are made with five different acids: acetic acid, malic acid, betaine, glycine, and N,N-((butyloxy)propyl) amino diacetic acid (BOPA). From the spectra of these titrations, the spectra of four types of water (acidic, basic, saline, and pure water) are subtracted, giving spectra with flat baselines without any artificial adjustment. Factor analysis (FA) made on the water-subtracted spectra yield the spectra of the principal species, and their abundances. Titration curves obtained from these precisely fit the theoretical curves and the pKa values in the literature. The remaining water bands that are not subtracted are assigned to water solute close-bound situations. The hydration number varied from 5 to 1, with an average of almost 2 per carboxyl carbonyl group. The IR CO band po...
416 citations
TL;DR: In this article, a powder and its thin film were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM) and IR spectra methods, which indicated that the ZnO particles crystallized in the wurtzite phase, which were well distributed in the films with the mean particle size of about 10nm.
Abstract: ZnO thin films were prepared by sol–gel dip coating method using zinc acetate dihydrate and 2-ethanolamine as the starting materials. The powder and its thin film were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM) and IR spectra methods. The results indicated that the ZnO particles crystallized in the wurtzite phase, which were well-distributed in the films with the mean particle size of about 10 nm. The IR spectra of the gel and powders annealed at different temperatures were investigated. It showed that the vibration bands of NH and mono-acetate diminished and the stretching mode of ZnO at 471 cm−1 appeared after the dried gel annealed at 500 °C for 1 h. The diameter, D of ZnO particles in the monolayer was also calculated from the optical spectroscopy curve, which is close to that obtained from AFM observation. The gas-sensing properties of the multi-layers for alcohols with different chain lengths were measured at room temperature. The thin films exhibited high sensitivity and rapid response–recovery characteristics to these gases. The film can detect methanol, ethanol and propyl alcohol vapor as low concentration as 1, 10, and 0.5 ppm, respectively.
355 citations
TL;DR: In this article, the influence of treatment with ammonia on adsorption properties toward CO2 was examined for commercially available CWZ-35 activated carbon for 2-h at elevated temperatures ranging from 200 to 1000°C.
348 citations
TL;DR: The modeling indicates that metal ions are partitioned between the exopolymer sheath and cell wall and that the carboxyl groups on the cyanobacterial cell wall are the dominant sink for metals at near neutral pH.
Abstract: In this study, we conducted synchrotron radiation Fourier transform infrared (IR) spectroscopy, potentiometric titration, and metal sorption experiments to characterize metal-cyanobacteria sorption reactions. Infrared spectra were collected with samples in solution for intact cyanobacterial filaments and separated exopolymeric sheath material to examine the deprotonation reactions of cell surface functional groups. The infrared spectra of intact cells sequentially titrated from pH 3.2 to 6.5 display an increase in peak intensity and area at 1400 cm(-1) corresponding to vibrational COO- frequencies from the formation of deprotonated carboxyl surface sites. Similarly, bulk acid-base titration of cyanobacterial filaments and sheath material indicates that the concentration of proton-active surface sites is higher on the cell wall compared to the overlying sheath. A three-site model provides an excellent fit to the titration curves of both intact cells and sheath material with corresponding pKa values of 4.7 +/- 0.4, 6.6 +/- 0.2, 9.2 +/- 0.3 and 4.8 +/- 0.3, 6.5 +/- 0.1, 8.7 +/- 0.2, respectively. Finally, Cu2+, Cd2+, and Pb2+ sorption experiments were conducted as a function of pH, and a site-specific surface complexation model was used to describe the metal sorption data. The modeling indicates that metal ions are partitioned between the exopolymer sheath and cell wall and that the carboxyl groups on the cyanobacterial cell wall are the dominant sink for metals at near neutral pH. These results demonstrate that the cyanobacterial surfaces are complex structures which contain distinct surface layers, each with unique molecular functional groups and metal binding properties.
341 citations
TL;DR: A new approach that combines electronic structure methods and molecular dynamics simulations to investigate the infrared spectroscopy of condensed phase systems is presented, and the methods presented are simple, and transferable to more complicated systems.
Abstract: We present a new approach that combines electronic structure methods and molecular dynamics simulations to investigate the infrared spectroscopy of condensed phase systems. This approach is applied to the OH stretch band of dilute HOD in liquid D2O and the OD stretch band of dilute HOD in liquid H2O for two commonly employed models of water, TIP4P and SPC/E. Ab initio OH and OD anharmonic transition frequencies are calculated for 100 HOD x (D2O)n and HOD x(H2O)n (n = 4-9) clusters randomly selected from liquid water simulations. A linear empirical relationship between the ab initio frequencies and the component of the electric field from the solvent along the bond of interest is developed. This relationship is used in a molecular dynamics simulation to compute frequency fluctuation time-correlation functions and infrared absorption line shapes. The normalized frequency fluctuation time-correlation functions are in good agreement with the results of previous theoretical approaches. Their long-time decay times are 0.5 ps for the TIP4P model and 0.9 ps for the SPC/E model, both of which appear to be somewhat too fast compared to recent experiments. The calculated line shapes are in good agreement with experiment, and improve upon the results of previous theoretical approaches. The methods presented are simple, and transferable to more complicated systems.
TL;DR: In this paper, the FT-Raman and FT-IR spectroscopy was used to characterize synthetic Mg/Zn/Al-hydrotalcites with atomic ratios of 6:0:2, 4:2 :2, 2:4:2 and 0:6:2.
Abstract: Synthetic Mg/Zn/Al-hydrotalcites with atomic ratios of 6:0:2, 4:2:2, 2:4:2 and 0:6:2 were characterized by FT-Raman and FT-IR spectroscopy. ‘AlOH’ IR translation modes are observed at 419, 427, 559, 616 and 771 cm−1 with two corresponding Raman bands at 465–477 and 547–553 cm−1. ‘MgOH’ IR translation modes are found at 412, 559 and 616 cm−1 with equivalent Raman bands at 464–477 and 547–553 cm−1. The ‘ZnOH’ IR translation mode is found at 445 cm−1 and the Raman modes around 450 and 495 cm−1. The CO32 − group is identified by the ν1(IR) at 1112 cm−1 and a doublet in the Raman around 1045–1055 and 1060 cm−1. ν2(IR) is observed at 874 cm−1. ν3(IR) is a doublet at 1359 and 1381 cm−1. ν4 is observed in both the IR and Raman spectra around 670 and 695–715 cm−1, respectively. In the OH deformation region, a doublet is observed for ‘AlOH’ at 955 and 1033 cm−1 in the IR spectra. The ‘ZnOH’ IR deformation mode is observed at 1462 cm−1. H2O is characterized by a bending mode at 1632 cm−1 and an H-bonded interlayer H2O mode at 3266 cm−1 with a Raman band between 3244 and 3271 cm−1. The OH stretching region is characterized by three bands in the Raman spectra around 3355–3360, 3440–3455 and 3535–3580 cm−1. One band is observed in the IR spectra at 3471 cm−1. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate.
Abstract: Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH2 or M(H2) molecules so formed react further to form higher MH4, (H2)MH2, or M(H2)2, and MH6, (H2)2MH2, or M(H2)3 hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.
TL;DR: In this article, the compositional properties of the layers were analyzed by FTIR and ATR infrared spectroscopy techniques, and a correlation between the N-H concentration and absorption loss was verified for silicon oxynitride slab waveguides.
TL;DR: The results show that 2D IR spectroscopy is more sensitive to structural differences between proteins than traditional infrared spectroscopic, providing an observable that allows comparison to quantitative models of protein vibrational spectroscology.
Abstract: We investigate the sensitivity of femtosecond Fourier transform two-dimensional infrared spectroscopy to protein secondary structure with a study of antiparallel β-sheets. The results show that 2D ...
TL;DR: In this study, a partial least squares (PLS) method was used to predict protein secondary structures from the protein IR spectra and the results correlate quite well with the data from X-ray studies, and the prediction from the amide III region is better than that from amid I or combined amide I and amideIII regions.
Abstract: Fourier transform infrared spectroscopy is becoming an increasingly important method to study protein secondary structure. The amide I region of the protein infrared spectrum is the widely used region, whereas the amide III region has been comparatively neglected due to its low signal. Since there is no water interference in the amide III region and, more importantly, the different secondary structures of proteins have more resolved differences in their amide III spectra, it is quite promising to use the amide III region to determine protein secondary structure. In our current study, a partial least squares (PLS) method was used to predict protein secondary structures from the protein IR spectra. The IR spectra of aqueous solutions of 16 different proteins of known crystal structure have been recorded, and the amide I, the amide III, and the amide I combined with the amide III region of these proteins were used to set up the calibration set for the PLS algorithm. Our results correlate quite well with the data from X-ray studies, and the prediction from the amide III region is better than that from amide I or combined amide I and amide III regions.
TL;DR: The vibrational spectra of the gaseous sodium complexes of glycine and proline provide the first experimental evidence that the salt bridge isomer is formed in the case of Pro-Na(+), and charge solvation by chelation of Na(+) between nitrogen and the carbonyl oxygen seems to be most favorable for Gly- Na(+).
Abstract: The vibrational spectra of the gaseous sodium complexes of glycine (Gly−Na+) and proline (Pro−Na+) have been recorded in the spectral range 1150−2000 cm-1. The complexes were formed by matrix-assisted laser desorption−ionization, introduced in the cell of a Fourier transform ion cyclotron resonance mass spectrometer, and their infrared spectra were recorded using photons of variable energy emitted by a free electron laser. Photon absorption was probed by the diminished intensity of the parent ion, due to its infrared-induced dissociation into bare sodium cation and the free amino acid and the appearance of Na+. The observed absorption bands are assigned using ab initio computations of the IR spectra of the lowest energy isomers in each case. They provide the first experimental evidence that the salt bridge isomer is formed in the case of Pro−Na+. In contrast, charge solvation by chelation of Na+ between nitrogen and the carbonyl oxygen seems to be most favorable for Gly−Na+, but a mixture of isomers canno...
TL;DR: A series of compounds, Li x FePO 4 (0 ≤ x ≤ 1), was prepared by chemical delithiation and investigated with Fourier transform infrared (FTIR) and Raman spectroscopy for the first time.
Abstract: A series of compounds, Li x FePO 4 (0 ≤ x ≤ 1), was prepared by chemical delithiation and investigated with Fourier transform infrared (FTIR) and Raman spectroscopy for the first time. Sample homogeneity with respect to Fe and P was analyzed with an electron microprobe. The imaging capabilities of the electron microprobe reveal larger-sized particles (10-20 μm diam) and fine intergranular particles (≤1 μm). Elemental analysis with the electron microprobe demonstrates that the Li x FePO 4 particles are relatively homogeneous. Thus, the electron microprobe may be used in conjunction with other instruments that are more commonly used to investigate particle morphology, such as scanning or transmission electron microscopes. Isotopic substitution experiments show that the symmetric and antisymmetric bending vibrations of the PO 3- 4 anion are highly mixed with Li + translatory vibrations. Consequently, no band in the IR spectrum of LiFePO 4 may be assigned solely as a lithium ion cage mode. Spectroscopic measurements of the Li x FePO 4 series demonstrate that the intramolecular modes of PO 3- 4 are particularly sensitive to the extraction of Li + ions from LiFePO 4 and the accompanying oxidation of Fe 2+ to Fe 3+ . Spectroscopic data suggest that the PO 3- 4 effective force constants (band frequencies), dipole moment derivatives (FTIR intensities), and polarizability derivatives (Raman intensities) change as LiFePO 4 is converted into FePO 4 , Together, the data strongly support the two-phase shell model of LiFePO 4 delithiation.
TL;DR: Infrared reflection absorption spectroscopy (IRAS) has been used to study CO adsorption on Au clusters ranging in size from 1.8 to 3.1 nm, supported on TiO(2), and the adsorbed CO vibrational frequency blue-shifts slightly and the heats of adsOrption increase sharply with decreasing cluster size.
Abstract: Infrared reflection absorption spectroscopy (IRAS) has been used to study CO adsorption on Au clusters ranging in size from 1.8 to 3.1 nm, supported on TiO2. The adsorbed CO vibrational frequency blue-shifts slightly (approximately 4 cm-1) compared to that adsorbed on bulk Au, whereas the heats of adsorption (−ΔHads) increase sharply with decreasing cluster size, from 12.5 to 18.3 kcal/mol.
TL;DR: In this paper, the authors describe 30 years of research on the surface properties of magnesium oxide, considered as the model prototype oxide of cubic structure, and compare the properties of single crystals, thin films and powdered samples (sintered at progressive higher temperatures) with the aim of demonstrating that the gap between “believed perfect” single crystal surfaces, typical of “pure” Surface Science, and high surface area samples, typically of Catalysis Science, can be progressively reduced.
TL;DR: In this paper, the IR spectra of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3hydroxyhexanoate), P(HB-Co-HHx) (HHx = 2.5, 3.4, and 12 mol %), and poly(PHB) (PHB = 0.
Abstract: Infrared (IR) spectra of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx = 2.5, 3.4, and 12 mol %), and poly(3-hydroxybutyrate) (PHB) were measu...
TL;DR: In this paper, the surface sum frequency generation vibrational spectroscopy (SFG-VS) was used as a polarization spectroscopic technique for vibrational spectral band assignment and orientational analysis for molecular groups at the interfaces.
Abstract: In this paper we report detailed examples of the surface sum frequency generation vibrational spectroscopy (SFG-VS) as a polarization spectroscopic technique for vibrational spectral band assignment and orientational analysis for molecular groups at the interfaces. Surface sum frequency generation vibrational spectroscopy (SFG-VS) has been widely used as an important spectroscopy probe for chemical bonding, structural conformation and molecular interactions of both fundamentally and technologically important interfaces. However, the potential for SFG-VS as a polarization spectroscopic technique is yet to be fully explored. In IR and Raman studies, polarized spectroscopy (PS) can provide information on molecular symmetries, which is necessary for accurate vibrational band assignment in complex chemical environments. We shall show that SFG-vibrational polarization spectroscopy (VPS) is the polarization spectroscopic tool on this purpose for the interface, along with its advantage of submonolayer sensitivity. This ability of SFG-VPS comes from the fact that vibrational bands from different symmetry types do not have strongest peak intensities in the same polarization configuration of the SFG-VPS spectra, because molecular groups are aligned or partially aligned at the interface. We chose to study the SFG-VPS of three diols, namely, ethylene glycol, 1,3-propanediol, and 1,5-pentanediol, at the vapor/liquid interfaces as model systems for the methylene-only molecules. The polarization analysis of the SFG spectra resulted in few explicit polarization selection rules or guidelines for the assignment of the CH stretching modes of the methylene groups. These results could be used to provide clarifications for some of the disagreements and controversies still exist in the literatures. These results can also shed light on the IR and Raman studies on methylene group in the bulk condensed phases.
TL;DR: In this paper, the effect of sodium promoter on cobalt-zinc oxide catalysts was studied in the steam reforming of ethanol between 523 and 723 K and characterized by transmission electron microscopy, X-ray diffraction, Raman and infrared spectroscopies.
TL;DR: A diagrammatic approach to incorporating all vibrational relaxation processes into the nonlinear response function is discussed, and how coherence transfer influences the analysis of structural variables from 2D IR spectroscopy is shown.
Abstract: Two-dimensional infrared (2D IR) spectroscopy of the symmetric and asymmetric C[Triple Bond]O stretching vibrations of Rh(CO)(2)acac in hexane has been used to investigate vibrational coherence transfer, dephasing, and population relaxation in a multilevel vibrational system The transfer of coherence between close-lying vibrational frequencies results in extra relaxation-induced peaks in the 2D IR spectrum, whose amplitude depends on the coherence transfer rate Coherence transfer arises from the mutual interaction of the bright CO stretches with dark states, which in this case reflects the mutual d-pi(*) back bonding of the Rh center to both the terminal carbonyls and the acetylacenonate ligand For 2D IR relaxation experiments with variable waiting times, coherent dynamics lead to the modulation of peak amplitudes, while incoherent population relaxation and exchange results in the growth of the relaxation-induced peaks We have modeled the data by propagating the density matrix with the Redfield equation, incorporating all vibrational relaxation processes during all three experimental time periods and including excitation reorientation effects arising from relaxation Coherence and population transfer time scales from the symmetric to the asymmetric stretch were found to be 350 fs and 3 ps, respectively We also discuss a diagrammatic approach to incorporating all vibrational relaxation processes into the nonlinear response function, and show how coherence transfer influences the analysis of structural variables from 2D IR spectroscopy
TL;DR: In this paper, the properties of surface hydroxyl species of diatomaceous silica are more similar to precipitated silica rather than fumed silica, and the Lewis (L) and Bronsted (B) acid sites were identified.
TL;DR: It is reported here that Hmd contains intrinsic CO bound to the Fe, and the effect of extrinsic (12)CO, (13) CO, ( 12)CN(-), and ( 13)CN(-) on the IR spectrum of Hmd.
Abstract: The iron−sulfur-cluster-free hydrogenase Hmd (H2-forming methylenetetrahydromethanopterin dehydrogenase) from methanogenic archaea has recently been found to contain one iron associated tightly with an extractable cofactor of yet unknown structure. We report here that Hmd contains intrinsic CO bound to the Fe. Chemical analysis of Hmd revealed the presence of 2.4 ± 0.2 mol of CO/mol of iron. Fourier transform infrared spectra of the native enzyme showed two bands of almost equal intensity at 2011 and 1944 cm-1, interpreted as the stretching frequencies of two CO molecules bound to the same iron in an angle of 90°. We also report on the effect of extrinsic 12CO, 13CO, 12CN-, and 13CN- on the IR spectrum of Hmd.
TL;DR: In this article, the authors demonstrate that scattering-type optical near-field microscopy features a spectral signature that differs characteristically from far-field absorption, and apply this signature to identify PMMA in the near field imaging of a nanostructured PMMA/PS polymer blend.
Abstract: We demonstrate—for a typical polymer vibrational infrared line—that scattering-type “apertureless” optical near-field microscopy features a spectral signature that differs characteristically from far-field absorption. Theory predicts a dispersion-like amplitude spectrum (besides an absorption-like, bell-shaped phase spectrum). This signature is experimentally verified for a vibrational resonance of PMMA, by probing with a CO laser tuned from 5.5 to 6 μm. We apply this signature to identify PMMA in the near-field imaging of a nanostructured PMMA/PS polymer blend, at <70nm resolution. Our results suggest a potentially quantitative chemometry based on near-field infrared vibrational fingerprints with spatial resolution that could reach 10 nm.
TL;DR: In this article, the structure of borohydrides MBH4 and their deuterides has been investigated by X-ray and neutron powder diffraction (M = K, Rb, Cs) and by infrared and Raman spectroscopy (M. = Na, K, rb, cb, N. Cs), and the properties of the overtones and combination bands, the Fermi resonance type interactions and the 10 Bt o 11 B splitting due to the presence of natural boron in the samples.
TL;DR: The reviewed state-of-the-art suggests this field is at an early stage of development with major open questions bearing on the surprising properties of the molecules and on the formation mechanisms, which are part of the challenge for the future.
Abstract: Progress in the study of a new class of chemically bound compounds of noble-gas atoms is reviewed. The focus is on rare-gas molecules of the form HNgY, where Ng is a noble-gas atom and Y is an electronegative group, prepared by photolysis of HY in the rare-gas matrix. Other related types of new molecules of noble-gas atoms are discussed as well. Topics discussed in this review include: (a) The nature of bonding and the energetic stability of the compounds. (b) The vibrational spectroscopy of the molecules, and its role in identification of the species. (c) The mechanism and dynamics of photochemical formation of HNgY in the matrix, and the pathways for thermal and infrared (IR)-induced decomposition. Specifically, attention is given to the issue of "direct" formation following photolysis of HY versus "delayed" formation involving H atom diffusion. (d) Molecules of the lighter rare gases Ar, Ne, and He, focusing on the experimentally prepared HArF and on theoretical predictions suggesting the existence of other molecules. (e) The most-recently discovered photochemically induced insertion compounds of Ng into hydrocarbons, such as HXeCCH. (f) Clusters of HNgY with other molecules. The possible existence of neat aggregates and crystals of HNgY. The reviewed state-of-the-art suggests this field is at an early stage of development with major open questions bearing on the surprising properties of the molecules and on the formation mechanisms. These are part of the challenge for the future.