Spectroscopic Characteristics of Differently Produced Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X‐ray absorption near edge structure, along with X‐ray photoemission by following the total valence bands and C 1s core‐level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp² hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence‐band X‐ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.     

Terahertz Time‐Domain Spectroscopy of Gases,Liquids, and Solids

The techniques and methods employed in the spectroscopic characterization of gases, liquids, and solids in the terahertz frequency range are reviewed. Terahertz time‐domain spectroscopy is applied to address a broadband frequency range between 100 GHz and 5 THz with a sub‐10 GHz frequency resolution. The unique spectral absorption features measured can be efficiently used in material identification and sensing. Possibilities and limitations of fundamental and industrial applications are discussed.     

Fluorescent perylene diimide rotaxanes: spectroscopic signatures of wheel-chromophore interactions

[2]- and [3]-rotaxanes with a tetraphenoxy perylene diimide core were synthesized. Hydrogen bonding between the wheel and the imide changes the optical properties of the perylene chromophore: the absorption and fluorescence spectra are red-shifted. The decay times of the rotaxanes are shorter in comparison with that of the axle. Single molecule fluorescence measurements reveal relatively narrow distributions of emission maxima and decay times. The averages are in agreement with ensemble measurements. The observed red shifts make the perylene diimide a suitable chromophore for sensing the position of the wheel on the axle.     

Structural Determination of a Photochemically Active Diplatinum Molecule by Time‐Resolved EXAFS Spectroscopy

Metallica : A large contraction of the Pt? Pt bond in the triplet excited state of the photoreactive [Pt₂(P₂O₅H₂)₄]^4? ion is determined by time‐resolved X‐ray absorption spectroscopy (see picture). The strengthening of the Pt? Pt interaction is accompanied by a weakening of the ligand coordination bonds, resulting in an elongation of the platinum–ligand bond that is determined for the first time.

     

Application of two‐dimensional near‐infrared (2D‐NIR) correlation spectroscopy to the discrimination of three species of Dendrobium

The objective of this paper was to apply two‐dimensional (2D) near‐infrared (NIR) correlation spectroscopy to the discrimination of three species of Dendrobium. Generalized 2D‐NIR correlation spectroscopy was able to enhance spectral resolution, simplify the spectrum with overlapped bands and provide information about temperature‐induced spectral intensity variations that was hard to obtain from one‐dimensional NIR spectroscopy. The FT‐NIR spectra were measured over a temperature range of 30–140°C. The 2D synchronous and asynchronous spectra showed remarkable differences within the range of 5600–4750 cm⁻¹ between different species of Dendrobium. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural and Vibrational Studies of Sr2[W(CN)8]·10H2O

The crystal structure of distrontium octacyanotungstate decahydrate, Sr₂[W(CN)₈] · 10H₂O, was solved using X‐ray single crystal diffraction. The tungsten atom lies on a two fold axis. Eight cyanide anions create tetragonal antiprismatic coordination sphere of tungsten atom. The two edge‐sharing tetragonal antiprisms of [Sr(NC)₃(OH₂)₅], create a dimer, [Sr₂(CN)₆(H₂O)₆(μ‐H₂O)₂], which lies on the inversion center. One symmetry independent water molecule is located in a void of 40 Å³. Vibrational (FT‐IR and FT‐Raman spectroscopic) behavior of main structural units is discussed. It was spectroscopically confirmed that the geometry of [W(CN)₈]^4– anion is slightly distorted from that corresponding to “free” anion. The number of observed bands is significantly lower than that expected for C₂ point group.     

Taking snapshots of photoexcited molecules in disordered media by using pulsed synchrotron X-rays

Photoexcited molecules are quintessential reactants in photochemistry. Structures of these photoexcited molecules in disordered media in which a majority of photochemical reactions take place remained elusive for decades owing to a lack of suitable X-ray sources, despite their importance in understanding fundamental aspects in photochemistry. As new pulsed X-ray sources become available, short-lived excited-state molecular structures in disordered media can now be captured by using laser-pulse pump, X-ray pulse-probe techniques of third-generation synchrotron sources with time resolutions of 30-100 ps, as demonstrated by examples in this review. These studies provide unprecedented information on structural origins of molecular properties in the excited states. By using other ultrafast X-ray facilities that will be completed in the near future, time-resolution for the excited-state structure measurements should reach the femtosecond time scales, which will make "molecular movies" of bond breaking or formation, and vibrational relaxation, a reality.     

Performance of fluorescence correlation spectroscopy for measuring diffusion and concentration.

Fluorescence correlation spectroscopy (FCS) has become an important tool for measuring diffusion, concentration, and molecular interactions of cellular components. The interpretation of FCS data critically depends on the measurement set-up. Here, we present a rigorous theory of FCS based on exact wave-optical calculations. Six of the most important optical and photophysical factors that influence FCS are studied: fluorescence anisotropy, cover-slide thickness, refractive index of the sample, laser-beam geometry, optical saturation, and pinhole adjustment. Our theoretical framework represents a general attempt to link all relevant parameters of the experimental set-up with the measured correlation function.     

Retrieval of spectral and dynamic properties from two-dimensional infrared pump-probe experiments

We have developed a fitting algorithm able to extract spectral and dynamic properties of a three level oscillator from a two-dimensional infrared spectrum (2D-IR) detected in time resolved nonlinear experiments. Such properties go from the frequencies of the ground-to-first and first-to-second vibrational transitions (and hence anharmonicity) to the frequency-fluctuation correlation function. This last is represented through a general expression that allows one to approach the various strategies of modeling proposed in the literature. The model is based on the Kubo picture of stochastic fluctuations of the transition frequency as a result of perturbations by a fluctuating surrounding. To account for the line-shape broadening due to pump pulse spectral width in double-resonance measurements, we supply the fitting algorithm with the option to perform the convolution of the spectral signal with a Lorentzian function in the pump-frequency dimension. The algorithm is tested here on 2D-IR pump-probe spectra of a Gly-Ala dipeptide recorded at various pump-probe delay times. Speedup benchmarks have been performed on a small Beowulf cluster. The program is written in FORTRAN language for both serial and parallel architectures and is available free of charge to the interested reader.     

Lab‐on‐a‐Chip Reactor Imaging with Unprecedented Chemical Resolution by Hadamard‐Encoded Remote Detection NMR

The development of microfluidic processes requires information‐rich detection methods. Here we introduce the concept of remote detection exchange NMR spectroscopy (RD‐EXSY), and show that, along with indirect spatial information extracted from time‐of‐flight data, it provides unique information about the active regions, reaction pathways, and intermediate products in a lab‐on‐a‐chip reactor. Furthermore, we demonstrate that direct spatial resolution can be added to RD‐EXSY efficiently by applying the principles of Hadamard spectroscopy.     

In‐Membrane Chemical Modification (IMCM) for Site‐Specific Chromophore Labeling of GPCRs

We present in‐membrane chemical modification (IMCM) for obtaining selective chromophore labeling of intracellular surface cysteines in G‐protein‐coupled receptors (GPCRs) with minimal mutagenesis. This method takes advantage of the natural protection of most cysteines by the membrane environment. Practical use of IMCM is illustrated with the site‐specific introduction of chromophores for NMR and fluorescence spectroscopy in the human κ‐opioid receptor (KOR) and the human A_2A adenosine receptor (A_2AAR). IMCM is applicable to a wide range of in vitro studies of GPCRs, including single‐molecule spectroscopy, and is a promising platform for in‐cell spectroscopy experiments.     

Revisiting the Solution Structure of Ceric Ammonium Nitrate

Ceric ammonium nitrate (CAN) is a single‐electron‐transfer reagent with unparalleled utility in organic synthesis, and has emerged as a vital feedstock in diverse chemical industries. Most applications use CAN in solution where it is assigned a monomeric [Ce^IV(NO₃)₆]^2? structure; an assumption traced to half‐century old studies. Using synchrotron X‐rays and Raman spectroscopy we challenge this tradition, converging instead on an oxo‐bridged dinuclear complex, even in strong nitric acid. Thus, one equivalent of CAN is recast as a two‐electron‐transfer reagent and a redox‐activated superbase, raising questions regarding the origins of its reactivity with organic molecules and giving new fundamental insight into the stability of polynuclear complexes of tetravalent ions.     

Expedited analysis of DFT outputs: Introducing moanalyzer

MOAnalyzer, a Matlab‐based program, has been developed to facilitate the analysis of density functional theory output files from ORCA. The program allows the user to define fragments within a molecule and then provides information on the contribution of each fragment to the molecular orbitals based on the Loewdin population analysis. Correlations to spectroscopy (X‐ray absorption and X‐ray emission) are also obtained, and the resulting information can be visualized in tables or MO diagrams. © 2012 Wiley Periodicals, Inc.     

Vibrational Spectroscopy of the Dehydrogenated Uracil Radical by Autodetachment of Dipole‐Bound Excited States of Cold Anions

Molecules with large enough dipole moments can bind an electron by the dipole field, which has little effect on the molecular core. A molecular anion can be excited to a dipole‐bound state, which can autodetach by vibronic coupling. Autodetachment spectroscopy of a complex anion cooled in a cryogenic ion trap is reported. Vibrational spectroscopy of the dehydrogenated uracil radical is obtained by a dipole‐bound state with partial rotational resolution. Fundamental frequencies for 21 vibrational modes of the uracil radical are reported. The electron affinity of the uracil radical is measured accurately to be 3.4810±0.0006 eV and the binding energy of the dipole‐bound state is measured to be 146±5 cm^?1. The rotational temperature of the trapped uracil anion is evaluated to be 35 K.     

Investigation of patinas formed on Chinese bronzes using modern multianalytical techniques

This paper presents an integrated study on nine natural Chinese bronze patinas without causing any damage to the bronze substrates, employing five modern analytical techniques including X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR) and Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP‐AES), and inductively coupled plasma mass spectrometry (ICP‐MS). Two artificial Chinese bronze patinas were also investigated by the same techniques for comparative purposes. As a result, XRD determined the chemical compositions of all selected samples and showed that the primary compound was malachite in natural soil environment under the general situation. Meanwhile, some interesting corrosion products such as gerhardtite and free copper were also observed. Three groups were classified according to the XRD results in order to provide a deeper insight into their spectroscopic characterization. Spectroscopic data of these patinas from FT‐IR and Raman spectroscopy are shown and interpreted in detail. ICP‐AES and ICP‐MS analyses provided valuable quantitative information, and made the study of the patinas more profound. Furthermore, all analytical results indicated that bronze patinas are extremely complex by virtue of the storage environment and their substrate alloys. The natural samples were rather heterogeneous and the artificial samples, especially the sample formed in the laboratory, were rather homogeneous of which the chemical constituents could be well defined. Copyright © 2007 John Wiley & Sons, Ltd.     

Local Structure of ZnO Micro Flowers and Nanoparticles Obtained by Micro‐Segmented Flow Synthesis

The micro‐segmented flow technique was applied for continuous synthesis of ZnO micro‐ and nanoparticles with short residence times of 9.4 s and 21.4 s, respectively. The obtained particles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Small angle X‐ray scattering (SAXS) and photoluminescence spectroscopy were used to determine the size and optical properties of ZnO nanoparticles. In addition, extended X‐ray absorption fine structure (EXAFS) spectroscopy was employed to investigate local structural properties. The EXAFS measurements reveal a larger degree of structural disorder in the nanoparticles than the microparticles. These structural changes should be taken into consideration while evaluating the size‐dependent visible emission of ZnO nanoparticles.