Search results for " Spectroscopy"
showing 10 items of 6851 documents
Tuning the Magnetic Properties of Carbon by Nitrogen Doping of Its Graphene Domains
2015
Here we present the formation of predominantly sp-coordinate carbon with magnetic- and heteroatom-induced structural defects in a graphene lattice by a stoichiometric dehalogenation of perchlorinated (hetero)aromatic precursors [hexachlorobenzene, CCl (HCB), and pentachloropyridine, NCCl (PCP)] with transition metals such as copper in a combustion synthesis. This route allows the build-up of a carbon lattice by a chemistry free of hydrogen and oxygen compared to other pyrolytic approaches and yields either nitrogen-doped or -undoped graphene domains depending on the precursor. The resulting carbon was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM…
Determination of mineral and trace element concentrations in pine needles by ICP-OES: evaluation of different sample pre-treatment methods
2008
In the present study, the determination of mineral and trace elements (Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) from pine needles using three sample pre-treatment methods followed by inductively coupled plasma optical emission spectrometry, was examined. Sample pre-treatment methods tested were microwave digestion, ultrasound-assisted digestion and dry ashing. The new ultrasound-assisted digestion method was optimised by the analysis of the standard reference material (SRM) 1575a (pine needles) sample. The speed of dry ashing method was significantly increased by ultrasound dissolution after ashing. All the ICP-OES measurements were performed in robust plasma conditions which were tested…
Yttrium Hydrido Complexes that Contain a Less “Constrained Geometry” Ligand: Synthesis, Structure, and Efficient Hydrosilylation Catalysis
2001
σ-Bond metathesis of the new linked amino-cyclopentadiene (C5Me4H)CH2SiMe2NHCMe3 with Y(CH2SiMe3)3(THF)2 gave the alkyl-yttrium complex [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(CH2SiMe3)(THF)] (1) in 66% yield. Compound 1 was characterized by NMR spectroscopy and X-ray crystal structure analysis. By hydrogenolysis, 1 was quantitatively converted into the dimeric hydride [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)(μ-H)]2 (2). X-ray crystal structure analysis revealed a Y2H2 core connected to two [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)] fragments in a skewed manner, with a relatively long yttrium−yttrium distance of 3.7085(8) A. In solution, two diastereomers were observed by 1H NMR spectroscopy at −78 °C. Dimer 2 was s…
On-line vapor-phase generation combined with Fourier transform infrared spectrometry
2008
We present a critical review of on-line vapor-phase generation combined with Fourier transform infrared spectrometry for detection. We discuss different experimental approaches developed for generating the vapor phase based on different principles (e.g., thermal volatilization, acid-base, redox reaction and covalent hydride generation). Using examples of applications, we try to demonstrate the analytical potential of on-line vapor-phase generation in vibrational spectrometry in order to improve the selectivity and the sensitivity of the measurement step and to make environmentally-friendly procedures available for problem solving in the analytical laboratory. We pay special attention to int…
Oxide/water interfaces: how the surface chemistry modifies interfacial water properties
2012
The organization of water at the interface with silica and alumina oxides is analysed using density functional theory-based molecular dynamics simulation (DFT-MD). The interfacial hydrogen bonding is investigated in detail and related to the chemistry of the oxide surfaces by computing the surface charge density and acidity. We find that water molecules hydrogen-bonded to the surface have different orientations depending on the strength of the hydrogen bonds and use this observation to explain the features in the surface vibrational spectra measured by sum frequency generation spectroscopy. In particular, 'ice-like' and 'liquid-like' features in these spectra are interpreted as the result o…
Crystal structure and IR spectrum of 1-O-α-d-glucopyranosyl-d-mannitol–ethanol (2/1)
1999
Abstract 1- O - α - d -Glucopyranosyl- d -mannitol–ethanol (2/1), (C 12 H 24 O 11 ) 2 –C 2 H 5 OH, crystallizes in the monoclinic space group P2 1 with unit cell dimensions a =11.4230(8) A, b =9.525(4) A, c =15.854(2) A, β =102.751(7)° and V =1682.4(7) A 3 , Z =2, D x =1.45 Mg m −3 , λ (Mo-K α )=0.71069 A, μ=0.128 mm −1 , F (000)=788 and T =293(2) K. The structure was solved by direct methods and refined by least-squares calculations on F 2 to R 1 =0.0371[ I >2 σ ( I )], and 0.0930 (all data, 3542 independent reflections, R int =0.021). There are two molecules of glucopyranosylmannitol (GPM) and one ethanol molecule in the asymmetric unit, and the glucopyranosyl ring adopts a chair conforma…
Structural and electronic contributions to hyperpolarizability in methyl p-hydroxy benzoate
2006
Abstract The single crystals of methyl p-hydroxy benzoate (MPHB) are grown from methanol solution by a low temperature solution growth technique. The SHG efficiency is tested using Q-switched Nd:YAG laser of wavelength λ at 1064 nm, which is approximately 1.2 times that of urea. Vibrational spectral analysis using NIR-FT Raman and FT-IR spectra is carried out to understand the structural and electronic contributions to hyperpolarizability in MPHB. The DFT computations are also performed at B3LYP/6-311G(d,p) level to derive equilibrium geometry, vibrational wavenumbers and intensities. The results of ab initio calculations at HF/6-311G(d,p) level show that the vibrational contribution for th…
Raman spectroscopy of acetic acid monomer and dimers isolated in solid argon
2011
Acetic acid (AA) monomer and its dimers were studied by means of Raman spectroscopy combined with the matrix isolation technique. All fundamental bands of CH3COOH monomer were identified, including the CH3 torsional mode. Additionally, three overtone or combination modes were observed as a result of their enhanced intensities by Fermi resonance (FR). Twenty bands of the cyclic dimer (C2h) were identified and assigned, among which appear all intermolecular modes. Bands due to two different higher energy forms of the dimer were also identified. The experimental assignments are supported by ab initio calculations. Copyright © 2011 John Wiley & Sons, Ltd.
Timolol derivatives. I. X-ray, NMR and theoretical studies of the crystallization of (S)-timolol O,O-diacetyl-l-tartaric acid monoester
1993
Abstract The absolute configurations of (S)-timolol hemihydrate and (S)-timolol O,O-diacetyl-(R,R)-tartaric acid monoester were determined by single crystal X-ray diffraction. An NMR analysis based on the temperature dependence of vicinal coupling constants was carried out to characterize the conformational behaviour of the S,R,R- and R,R,R-forms in solution. The same conformation as in crystalline state was also found in solution, although with a rather low preference over some other conformations. Results of theoretical calculations using MNDO and AMBER force field methods are reported. An infinite chain of hydrogen bonds, along with other favourable inter- and intramolecular forces that …
Various types of polysiloxanes studied by positron annihilation lifetime spectroscopy
2014
Abstract In the work, linear poly(vinylsiloxanes) with regular distributions of vinyl groups along chains, the networks obtained by their hydrosilylation with various hydrogensiloxanes, products of pyrolysis of such networks as well as the networks prepared via reaction of low-molecular siloxanes have been studied by positron anihilation lifetime spectroscopy (PALS). Based on free volume sizes determined by this method, relations between cross-link densities in the investigated systems have been established. They have been compared with the results of swelling experiments conducted in the work and to efficiency of cross-linking reaction evaluated in our previous FTIR investigations of the s…