Search results for " Spectroscopy"
showing 10 items of 6851 documents
Inelastic and quasi-elastic light scattering in (NaCN)1?x(KCN)x quadrupolar glasses
1990
The elastic constantsc11 andc44, and the attenuation of longitudinal phonons along (100)-direction in (NaCN)1−x(KCN)x mixed crystals have been determined by brillouin spectroscopy in the temperature range fromT=10K−300K. Minima inc44 (T) which determine the freezing tempratureTF in these orientational glasses appear at lower temperatures compared to neutron scattering results. The coupling of molecular reorientations to longitudinal phonons in NaCN-rich smaples shows up in dispersion effects inc11 (T) and the appearence of a dynamical central peak nearTF.
Line mixing in the stimulated Raman spectrum of the ν1 band of SiH4 at 0.4–1.0 bar
1993
The stimulated Raman spectrum of the ν1 band of SiH4 has been recorded at 0.4 and 1.0 bar pressures and room temperature. Line mixing of the fine structure components of this spectrum was taken into account in a calculated profile by considering coupling between the main transitions and using a simple model (strong collision model, SCM) for the relaxation matrix.
Effects of high-pressure on the structural, vibrational, and electronic properties of monazite-type PbCrO4
2012
We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of PbCrO 4 (the mineral crocoite) at ambient and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. X-ray-diffraction, Raman, and optical absorption experiments have allowed us also to completely characterize two pressure-induced structural phase transitions. The first transition is from a monoclinic structure to another monoclinic structure. It maintains the symmetry of the crystal but has important consequences in the physical properties; among others, a band-gap collapse is induced. The second one invo…
Removal of Escherichia coli from Saturated Sand Columns Supplemented with Hydrochar Produced from Maize
2014
Despite numerous studies on hydrochar use, its application in water treatment for pathogen removal remains unexplored. In this study, we evaluated the efficiency of hydrochar produced from crop residue of maize for water treatment by determining Escherchia coli breakthrough from sand columns supplemented with hydrochar. To enhance the adsorptive capacity, raw hydrochar was activated by 1 mol L⁻¹ KOH at room temperature. The experiments conducted in a 10-cm sand bed with 1.5% (w/w) activated and raw hydrochar supplements, not activated by KOH, showed 93 and 72% of E. coli removal efficiencies, respectively. Activation of KOH not only enhanced the E. coli removal but also increased the streng…
Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence
2014
Guanter, Luis et al.
Temperature effects on the performances of the ATHENA X-IFU thermal filters
2016
The X-Ray Integral Field Unit (X-IFU) detector on-board ATHENA is an array of TES micro-calorimeters that will operate at ~50 mK. In the current investigated design, five thermal filters (TF) will be mounted on the cryostat shields to attenuate IR radiative load and avoid energy resolution degradation due to photon shot noise. Each filter consists of a thin polyimide film (~50 nm thick) coated with aluminum (~30 nm thick). Since the TF operate at different temperatures in the range 0.05-300 K, it is relevant to study how temperature affects their mechanical/optical performances (e.g. near edge absorption fine structures of the atomic elements in the filter material). Such results are crucia…
On-line Mössbauer measurements at low temperatures of 83mKr implanted into Al
1978
Abstract A vacuum ion implantation chamber housing a helium flow cryostat and a Mossbauer transducer has been constructed and coupled directly to an ion separator for low temperature implantation and on-line Mossbauer measurements. 83m Kr, produced by thermal neutron activation of enriched 82 Kr gas, has been implanted into Al foils in the temperature range 15–300 K. Annealing effects and the temperature dependence of the Lamb-Mossbauer factor have been studied by Mossbauer measurements (at 15–35 K) using the implanted Al targets as sources and Kr/hydrochinone as absorber.
A Mössbauer cryostat equipped with a Gifford McMahon cryocooler
1989
A new cryostat for Mossbauer spectroscopic measurements has been developed around a cryogenerator of the Gifford McMahon type operating with helium gas in a closed circuit. Both source and absorber can be cooled to about 30K and the unwanted vibrations caused by the helium compression/expansion cycle have been limited to approximately 0.05–0.06 mms−1.
Kinetic control in the chiral recognition of three-bladed propellers
2010
The ion pair of the stereolabile C(3)-symmetric, i(+)o proton complex [1H](+) of diaza-macropentacycle 1 and the configurationally stable Delta-TRISPHAT ([Delta-3](-)) anion exists in the form of two diastereomers, namely, [Delta-(1.H)][Delta-3] and [Lambda-(1.H)][Delta-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D(8)]THF (28%)CD(2)Cl(2) (22%)CDCl(3) (20%)[D(8)]toluene (16%)C(6)D(6) (7%)[D(6)]acetone (0%) at thermodynamic equilibrium. Except in the case of [D(6)]acetone, the latter is reached after a period of time that increases from 1 h ([D(8)]THF) to 24 h (CDCl(3)). Moreover, the initial value of the de of [1.H][Delta-3] in CDCl(3), before the t…
Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties
2019
International audience; The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4)2·xH2O led to the complex [Fe(L6)](ClO4)2 (1), which was characterized as the first Fe(II) complex based on the unsymmetrical N-functionalized tacn ligand. The crystal structure revealed a discrete monomeric [FeL6]2+ entity in which the unsymmetrical N-functionalized triazacyclononane molecule (L6) acts as hexadentate ligand. As …