Search results for " density"
showing 10 items of 2709 documents
First‐principles modelling of defects in advanced nuclear fuels
2007
In this paper we present and discuss the results of first first-principle modelling of point defects in nitride nuclear fuels. Calculations have been performed using the VASP computer code combined with supercells containing up to 250 atoms. The effective atomic charges, the electronic density redistribution, atomic displacements around U and N vacancies and their formation energies are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers
2021
Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn–syn, syn–anti, and anti–anti) were studied. A reliable preparation of radical cations and dications using antimony pentachloride as an oxidant gives deeply colored salts. The electronic structure of the radical cations was assessed by EPR spectroscopy, whereas dicationic structures were characterized by NMR spectroscopy. In addition, a deeper insight into the electronic structure was experimentally and computationally obtained by UV/Vis spectroscopy …
Methylium Ions with OPV Chains − New NIR Dyes
2001
Carbinols, which contain three OPV chains, were generated in convergent syntheses. The extension of the conjugation leads to a bathochromic effect that shifts the absorption from the UV into the visible region. The carbinol series has a convergence limit of the absorption at λmax = 415 nm. The corresponding carbenium ions exhibit a stronger bathochromic shift with the increasing number of repeating units in each chain. Thus, NIR dyes were obtained which show a convergence limit at λmax = 879 nm. The charge distribution in the ground state of the carbocations is discussed on the basis of 13C NMR spectroscopic data.
Graphical representation of polynuclear acid-base and complex equilibria.
1983
Abstract A calculation procedure for diagrams of log CM = ƒ(pL) at various values of the ratio of analytical concentrations, CL/CM, in polynuclear binary systems is described. The diagrams are useful in the resolution of analytical problems of practical interest involving acid-base equilibria (such as the preparation of buffer solutions) and complex equilibria. The presence of a solid phase is also considered.
Molecular scale structure and dynamics at an ionic liquid/electrode interface.
2017
After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion-ion correlations dominating the liquid bulk structure.…
High-resolution photoacoustic Raman spectroscopy of gases
1992
A high-resolution photoacoustic Raman spectroscopy experiment is described. The resolution achieved by using two single-mode pulsed lasers is about 0.0054 cm −1 (full width at half maximum intensity). The experiment was tested first on the v 1 /2v 2 bands of CO 2 and gave an increase of at least about one order of magnitude in the signal-to-noise ratio with respect to stimulated Raman spectroscopy at low pressure (ca. 10 Torr ≃ 1.3 kPa). The sensitivity is also demonstrated by the study of the weak hot band v 1 +v 2 −v 2 of CO 2 . In both cases, the experimental line shape is well reproduced by taking into account Doppler and collisional effects. A comparison with CARS spectra was also made
Analysis of Active-Site Distribution in ZSM-5 Crystals by Infrared Microscopy
1993
Abstract The acid Site distribution over large ZSM-5 crystals was analyzed using FTIR microscopy. Results of the analysis of the OH-stretching vibrations and of vibrations of pyridine adsorbed on Bronsted and Lewis acid sites were found to be in good agreement. The resolution which can be obtained using this novel technique is about 10-20 μm. This limits the application to large crystals as analyzed in this study. Comparison of the results of IR microscopy with aluminum distributions obtained by electron microprobe analysis revealed that IR microscopy cannot resolve inhomogeneities on a scale smaller than the above-stated limits. The results of both methods on a larger scale, however. are i…
Spectral investigation of spin echo emission
1993
Abstract The spectral content of the echo radiation emitted after a two-pulse sequence is measured in a two-level spin system. The spectral profiles exhibit maxima and zeroes of spectral density depending on the exciting sequence parameters. A calculation based on a vectorial model relates the zeroes to those packets that happen to be transparent to the second (refocusing) pulse. Moreover we report on a new spectral narrowing effect which we tentatively ascribe to the instantaneous diffusion.
A pH-tunable nanofluidic diode: electrochemical rectification in a reconstituted single ion channel.
2006
We report pH-dependent electrochemical rectification in a protein ion channel (the bacterial porin OmpF) reconstituted on a planar phospholipid membrane. The measurements performed at single-channel level show that the electric current is controlled by the protein fixed charge and it can be tuned by adjusting the local pH. Under highly asymmetric pH conditions, the channel behaves like a liquid diode. Unlike other nanofluidic devices that display also asymmetric conductance, here the microscopic charge distribution of the system can be explored by using the available high-resolution (2.4 A) channel crystallographic structure. Continuum electrostatics calculations confirm the hypothesized bi…
Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV
2000
During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refineme…