Showing papers on "Fourier transform spectroscopy published in 2010"

Cavity-enhanced dual-comb spectroscopy

Abstract: The sensitivity of molecular fingerprinting is dramatically improved when the absorbing sample is placed in a high-finesse optical cavity, because the effective path length is increased. When the equidistant lines from a laser frequency comb are simultaneously injected into the cavity over a large spectral range, multiple trace gases may be identified1 within a few milliseconds. However, efficient analysis of the light transmitted through the cavity remains challenging. Here, a novel approach—cavity-enhanced, frequency-comb, Fourier-transform spectroscopy—fully overcomes this difficulty and enables measurement of ultrasensitive, broad-bandwidth, high-resolution spectra within a few tens of microseconds without any need for detector arrays, potentially from the terahertz to ultraviolet regions. Within a period of just 18 µs, we recorded the spectra of the ammonia 1.0 µm overtone bands comprising 1,500 spectral elements and spanning 20 nm, with a resolution of 4.5 GHz and a noise equivalent absorption at 1 s averaging of 1 × 10−10 cm−1 Hz−1/2, thus opening a route to time-resolved spectroscopy of rapidly evolving single events. By combining Fourier transform spectroscopy with two frequency-shifted combs and cavity ring-down spectroscopy, scientists demonstrate a powerful new tool for ultrahigh sensitivity spectroscopy. The scheme can measure broadband, high-resolution spectra in tens of microseconds, does not require detector arrays and may allow tuning from terahertz to ultraviolet frequencies.

Secondary structure of food proteins by Fourier transform spectroscopy in the mid-infrared region

Abstract: Fourier transform spectroscopy in the mid-infrared (400–5,000 cm−1) (FT-IR) is being recognized as a powerful tool for analyzing chemical composition of food, with special concern to molecular architecture of food proteins. Unlike other spectroscopic techniques, it provides high-quality spectra with very small amount of protein, in various environments irrespective of the molecular mass. The fraction of peptide bonds in α-helical, β-pleated sheet, turns and aperiodic conformations can be accurately estimated by analysis of the amide I band (1,600–1,700 cm−1) in the mid-IR region. In addition, FT-IR measurement of secondary structure highlights the mechanism of protein aggregation and stability, making this technique of strategic importance in the food proteomic field. Examples of applications of FT-IR spectroscopy in the study of structural features of food proteins critical of nutritional and technological performance are discussed.

Mid-infrared Fourier transform spectroscopy with a broadband frequency comb.

Abstract: We present a first implementation of optical-frequency-comb-based rapid trace gas detection in the molecular fingerprint region in the mid-infrared Near-real-time acquisition of broadband absorption spectra with 00056 cm(-1) maximum resolution is demonstrated using a frequency comb Fourier transform spectrometer which operates in the 2100-to-3700-cm(-1) spectral region We achieve part-per-billion detection limits in 30 seconds of integration time for several important molecules including methane, ethane, isoprene, and nitrous oxide Our system enables precise concentration measurements even in gas mixtures that exhibit continuous absorption bands, and it allows detection of molecules at levels below the noise floor via simultaneous analysis of multiple spectral features

High field dynamic nuclear polarization—the renaissance

Abstract: Sensitivity is a critical issue in NMR spectroscopy, microscopy and imaging, and the factor that often limits the success of various applications. The origin of low sensitivity in NMR is well known to be due to the small magnetic moment of nuclear spins, which yields small Boltzmann polarizations and weak absorption signals. Historically, each advance in technology and methodology that has increased the signal-to-noise in NMR has shifted the boundary of what is achievable, often opening new areas of application and directions of research. The archetypal example of this phenomenon was the introduction of Fourier transform spectroscopy which led to increases of ∼ 102-fold in signal-to-noise, revolutionizing NMR and many other forms of spectroscopy.1 More recent technological developments of note include the continuing development of higher field superconducting magnets which increases polarization, and cryoprobes in which the excitation/detection coil is maintained at low temperatures increasing sensitivity through a higher probe Q and decreasing receiver noise.2 In addition, innovations in NMR methodology have improved sensitivity, classic examples being Hartmann–Hahn cross polarization,3,4 and J-coupling meditated5 transfer methods, and the introduction of 1H detection of 13C/15N resonances.6 Furthermore, techniques for non-inductive detection of resonance, such as the AFM-based technique of magnetic resonance force microscopy (MRFM), have recently allowed observation of a single electron spin,7 and ∼ 100 nuclear spins/√Hz.8

Effect of Different Solvent Ratios (Water/Ethylene Glycol) on the Growth Process of CaMoO4 Crystals and Their Optical Properties

Abstract: In this paper, calcium molybdate (CaMoO4) crystals (meso- and nanoscale) were synthesized by the coprecipitation method using different solvent volume ratios (water/ethylene glycol). Subsequently, the obtained suspensions were processed in microwave-assisted hydrothermal/solvothermal systems at 140 °C for 1 h. These meso- and nanocrystals processed were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet−visible (UV−vis) absorption spectroscopies, field-emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these meso- and nanocrystals have a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 827 cm−1, which is associated with the Mo−O antisymmetric stretching vibrations into the [MoO4] clusters. FEG-SEM micrographs...

Mid-infrared dual-comb spectroscopy with 2.4 μm Cr2+:ZnSe femtosecond lasers

Abstract: The mid-infrared part of the electromagnetic spectrum is the so-called molecular fingerprint region because gases have tell-tale absorption features associated with molecular rovibrations. This region can be for instance exploited to detect small traces of environmental and toxic vapors in atmospheric and industrial applications. Novel Fourier-transform spectroscopy without moving parts, based on time-domain interferences between two comb sources, can in particular benefit optical diagnostics and precision spectroscopy. To date, high-resolution and -sensitivity proof-of-principle experiments have only been reported in the near-infrared region where frequency-comb oscillators are conveniently available. However, as most of the molecular transitions in this region are due to weak overtone bands, this spectral domain is not ideal for sensitive and rapid detection. Here we present a proof-of-principle experiment of frequency-comb Fourier-transform spectroscopy with two Cr2+:ZnSe femtosecond oscillators directly emitting in the 2.4 μm mid-infrared region. The acetylene absorption spectrum in the region of the $ u_{1}+ u_{5}^{1}$ band, extending from 2370 to 2525 nm, could be recorded within a 10 μs acquisition time without averaging with 12 GHz resolution.

Automated broadband phase correction of Fourier transform ion cyclotron resonance mass spectra.

Abstract: It has been known for 35 years that phase correction of FTICR data can in principle produce an absorption-mode spectrum with mass resolving power as much as a factor of 2 higher than conventional magnitude-mode display, an improvement otherwise requiring a (much more expensive) increase in magnetic field strength. However, temporally dispersed excitation followed by time-delayed detection results in steep quadratic variation of signal phase with frequency. Here, we present a robust, rapid, automated method to enable accurate broadband phase correction for all peaks in the mass spectrum. Low-pass digital filtering effectively eliminates the accompanying baseline roll. Experimental FTICR absorption-mode mass spectra exhibit at least 40% higher resolving power (and thus an increased number of resolved peaks) as well as higher mass accuracy relative to magnitude mode spectra, for more complete and more reliable elemental composition assignments for mixtures as complex as petroleum.

Resonance lineshapes in two-dimensional Fourier transform spectroscopy

Abstract: We derive an analytical form for resonance lineshapes in two-dimensional (2D) Fourier transform spectroscopy. Our starting point is the solution of the optical Bloch equations for a two-level system in the 2D time domain. Application of the projection-slice theorem of 2D Fourier transforms reveals the form of diagonal and cross-diagonal slices in the 2D frequency data for arbitrary inhomogeneity. The results are applied in quantitative measurements of homogeneous and inhomogeneous broadening of multiple resonances in experimental data.

Structural and optical properties of unannealed and annealed zno nanoparticles prepared by a chemical precipitation technique

Abstract: In this paper we report the structural, electronic and optical properties of ZnO nanocrystals synthesized by a facile chemical method. ZnO nanoparticles prepared by this method were investigated employing X-ray diffraction (XRD), Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform infrared (FTIR), UV–Visible and Fluorescence (FL) spectroscopy. In order to study the effect of annealing on ZnO nanoparticles, we have analyzed pre- and post-annealed nanoparticles. It was observed that annealing treatment removes the impurities and consequently enhances the purity of ZnO nanoparticles without influencing their wurtzite phase. The absorption and excitation transitions occurring in annealed ZnO nanoparticles are similar to those in unannealed ZnO; however, some fluorescence emissions are altered. On the one hand, annealing assists in obtaining the pure ZnO nanoparticles without affecting their size and crystal structure; on the other hand channels of radiative combination are affected by the annealing process.

Enrichment, resolution, and identification of nickel porphyrins in petroleum asphaltene by cyclograph separation and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry.

Abstract: We report here the first high resolution mass spectrometric evidence of nickel porphyrins in petroleum. A petroleum asphaltene sample is fractionated by a silica-gel cyclograph. Nickel content is enriched by ∼3 fold in one of the cyclograph fractions. The fraction is subsequently analyzed by atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with an average mass resolving power of over 500 K (M/ΔMfwhm). Similar to vanadyl porphyrins, monocylcoalkano-type (presumed to be deocophylerythro-etioporphyrin DPEP) Ni porphyrins are found to be the most abundant family followed by etio, bicycloalkano-type, and rhodo-monocylcoalkano-type Ni porphyrins. A Z number ranging from −28 to −44 and a carbon number ranging from 26 to 41 were observed. A significant amount of nickel and vanadyl geoporphyrins are in more condensed tetrapyrrolic cores than just chlorophyll-derived DPEP- and etioporphyrins. Ni has a higher etio/DPEP ratio and rhodo-etio/rhodo-DPEP ...

Multi-Wavelength Optical Fiber Refractive Index Profiling by Spatially Resolved Fourier Transform Spectroscopy

Abstract: A non-destructive technique to measure an optical fiber's refractive index profile with sub-?m spatial resolution over a wavelength range spanning more than one octave (from 480 to 1040 nm) in a single measurement is described. Data showing the variation of refractive index with wavelength for several fiber types is presented.

A strategy for the determination of the elemental composition by fourier transform ion cyclotron resonance mass spectrometry based on isotopic peak ratios

Abstract: We propose a novel strategy for determining the elemental composition of organic compounds using the peak ratio of isotopic fine structure observed by high-magnetic field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Using 3′-phosphoadenosine 5′-phosphosulfate and CTU guanamine as standard organic compounds, isotopic peaks derived from 15N-, 34S-, and 18O-substituted forms were separated from 13C-substituted species. Furthermore, these isotopic peaks were quantitatively detected and closely matched the natural abundance of each element. These data successfully led us to determine the one elemental composition in a standard independent manner. The approach should be particularly amenable to the metabolomics research field.

Synthesis And Characterization Of Highly Crystalline Polyaniline Film Promising For Humid Sensor

Abstract: Polyaniline (PANI) was prepared in emeraldine via chemical oxidation method using CuSO4 as initiating agent. The chemical characterizations were made using UV-vis (ultraviolet-visible spectrophotometry), FT-IR (Fourier transform spectroscopy), TG- DTA (thermo-gravimetric/differential thermal analysis), ESI-MS (electrospray ionization mass spectrometry), XRD (X-ray diffraction), SEM (scanning electron microscopy) techniques. The results revealed the formation of homogeneous, crystalline PANI with sub-micron size particles. The PANI thin film of 0.5 µm thickness has been fabricated using spin coating technique. The resulting PANI film was exposed to controlled humid condition and change in resistance has been recorded. The resistance was continuously decreased from 13.5 to 3.75 MΩ with a linear change in humidity ranging from 3 to 95%. The result was reproducible and checked by repeating observation. Copyright © 2010 VBRI press.

Characterization of Proton Transfer in Co-Crystals by X-ray Photoelectron Spectroscopy (XPS)

Abstract: Characterization at the molecular level establishes X-ray photoelectron spectroscopy (XPS) as a useful technique for determining the extent of proton transfer in molecular crystals by studying theophylline-citric acid co-crystals alongside solid-state nuclear magnetic resonance (ssNMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). A complex has been formed by milling theophylline with either anhydrous or monohydrate citric acid and established as a 1:1 co-crystal by a combination of both conventional and novel analytical methods. The absence of peaks from the starting materials in the X-ray diffraction powder pattern indicates that the product was formed quantitatively, with elemental analysis and XPS revealing a 1:1 stoichiometry. Thermogravimetric analysis demonstrated the complex was anhydrous, with differential scanning calorimetry showing a melting temperature different from that of the starting materials. The absence of a C═NH+ N1s peak in XPS and the small mag...

A multispectroscopic structural study of lead silicate glasses over an extended range of compositions

Abstract: A series of lead silicate glasses, spanning the broadest reported range of lead contents (up to 83 mol% PbO), were prepared, on which the following spectroscopic observations were made: 29Si magic angle spinning nuclear magnetic resonance, time of flight mass spectroscopy, raman spectroscopy and fourier transform infrared spectroscopy. For bulk, splat-quenched samples, infrared results indicate that the lever rule is approximately followed until about 60 mol% PbO, though with considerable dissociation of the stoichiometric groups into silicate units with lesser and greater numbers of non-bridging oxygens. For roller-quenched samples, nuclear magnetic resonance data are consistent with a statistical distribution up to this lead concentration. Above 60 mol% PbO, added oxygen remains associated with lead to form a separate lead oxide glass network. The evidence for this comes from each of the spectroscopic techniques employed. A quantitative distribution of PbO is given.

Analytical strategies for characterizing the surface chemistry of nanoparticles.

Abstract: Chemical modifications of nanoparticle (NP) surfaces are likely to regulate their activities, remove their toxic effects, and enable them to perform desired functions. It is urgent to develop analytical strategies for acquiring structural and quantitative information about small molecules linked to the surface of NP. Recent progress in characterizing the surface chemistry of NPs using nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, liquid chromatography-mass spectroscopy (LC-MS), X-ray photoelectron spectroscopy (XPS), and combustion elemental analysis are reviewed.

Thermodynamics and Nucleation Kinetics of m-Aminobenzoic Acid Polymorphs

Abstract: The polymorphism of m-aminobenzoic acid has been investigated. Two polymorphs have been identified and characterized by X-ray powder diffraction (XRPD), Fourier transform IR (FTIR), microscopy, and ...

The 1S+1S asymptote of Sr2 studied by Fourier-transform spectroscopy

Abstract: An experimental study of the long range behavior of the ground state X1Σ+ g of Sr2 is performed by high resolution spectroscopy of asymptotic vibrational levels and the use of available photoassociation data. Ground state levels as high as v’’=60 (outer turning point at 23 A and 0.1 cm-1 below the asymptote) could be observed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation of the v’=4, J’=9 rovibrational level of the state 21Σ+ u. A precise value of the scattering length for the isotopologue 88Sr2 is derived and transferred to all other isotopic combinations by mass scaling with the given potential. The derived potential together with already published information about the state 21Σ+ u directs to promising optical paths for producing cold molecules in the electronic ground state from an ultracold ensemble of Sr atoms.