Search results for "Theoretical"
showing 10 items of 11439 documents
Substituent effect on ammonia–borane donor–acceptor complexes: a G2(MP2) molecular orbital study
1998
Abstract H3BNHnMe3−n and Me3−nHnBNH3 (n=0–3) donor–acceptor complexes have been studied using the G2(MP2) method. Predicted equilibrium structures and dissociation energies have been correlated to the degree of substitution on the donor and the acceptor separately. It is found that successive methyl substitutions on boron reduce the dissociation energies of the complexes, contrary to the successive substitutions on nitrogen. The NBO partitioning scheme suggests that there is no correlation between the charge transfer and the dissociation energies. These results are interpreted in terms of the changes in the HOMO−LUMO gap, the type of acceptor and donor involved, and distortion of the accept…
Templated growth of smart nanocomposite thin films: Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition of vanadyl acetylacet…
2009
Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition methodology has been utilised to produce nanocomposite thin films of gold nanoparticles and vanadium dioxide from vanadyl acetylacetonate and auric acid. The addition of tetraoctyl ammonium bromide (TOAB) to the precursor Solution gave control of the size and distribution of gold nanoparticles in the vanadium oxide matrix. These reactions led to vanadium dioxide films with reduced crystallite sizes and enhanced thermochromic properties. The films were analysed by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Their optical and thermochromic behaviour was also determined, This h…
Selective Extraction and Efficient Binding in a Protic Solvent of Contact Ion Triplets by Using a Thiourea-Based Bis-Calix[6]arene Receptor
2013
We report a D3h-symmetric tail-to-tail bis-calix[6]thiourea 5 that displays two divergent cavities triply connected by thiourea linkages. This calix[6]tube was efficiently synthesized through a [1+1] macrocyclization reaction and characterized by X-ray diffraction analysis. The binding properties of this heterotritopic receptor were evaluated in a protic environment (i.e., CD3OD/CDCl3) through NMR studies. Thus, bis-calix[6]thiourea 5 exhibits a remarkable ability in the cooperative complexation of an anion sandwiched between two ammonium ions, a high selectivity for ammonium sulfate salts being observed. The anion is bound through multiple hydrogen-bonding interactions at the thiourea bind…
Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects.
2016
Dicarbonyls are known to be important precursors of so-called atmospheric brown carbon, significantly affecting aerosol optical properties and radiative forcing. In this systematic study we report the formation of light-absorbing nitrogen containing compounds from simple 1,2-, 1,3-, 1,4-, and 1,5-dicarbonyl + amine reactions. A combination of spectrophotometric and mass spectrometric techniques was used to characterize reaction products in solutions mimicking atmospheric particulates. Experiments with individual dicarbonyls and dicarbonyl mixtures in ammonium sulfate and glycine solutions demonstrate that nitrogen heterocycles are common structural motifs of brown carbon chromophores formed…
Solution synthesis of nanoparticular binary transition metal antimonides
2011
The preparation of nanoengineered materials with controlled nanostructures, for example, with an anisotropic phase segregated structure or a regular periodicity rather than with a broad range of interparticle distances, has remained a synthetic challenge for intermetallics. Artificially structured materials, including multilayers, amorphous alloys, quasicrystals, metastable crystalline alloys, or granular metals, are mostly prepared using physical gas phase procedures. We report a novel, powerful solution-mediated approach for the formation of nanoparticular binary antimonides based on presynthesized antimony nanoparticles. The transition metal antimonides M-Sb (M = Co, Ni, Cu(2), Zn) were …
Amplified Spontaneous Emission Properties of Solution Processed CsPbBr3 Perovskite Thin Films
2017
Metal halide perovskites are currently emerging as highly promising optoelectronic materials. It has been recently demonstrated that fully inorganic solution processed CsPbBr3 perovskite thin films show good electroluminescence properties combined with high thermal stability. In this work, we investigate in details the amplified spontaneous emission (ASE) properties of CsPbBr3 perovskite thin films, as a function of the temperature and the trap density, modified by changing the CsBr-PbBr2 precursor concentration. ASE is observed in samples from both CsBr-rich solution (low trap density) and equimolar solution (higher trap density), up to about 150 K, with a minimum threshold of 26 and 29 mu…
Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X = Br, I) Perovskite Nanocrystals
2019
CsPbX3 perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. However, a better understanding of the physical mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or electrical excitation). Here, we establish the intrinsic mechanisms underlying ASE in PNCs of three different band gaps (CsPbBr3, CsPbBr1.5I1.5, and CsPbI3). Our characterization at cryogenic temperatures does not reveal any evidence of the biexciton mechanism in the formation of ASE. Instead, the measured …
Optical gain, spontaneous and stimulated emission of surface plasmon polaritons in confined plasmonic waveguide
2010
International audience; We develop a theoretical model to compute the local density of states in a confined plasmonic waveguide. Based on this model, we derive a simple formula with a clear physical interpretation for the lifetime modification of emitters embedded in the waveguide. The gain distribution within the active medium is then computed following the formalism developed in a recent work [Phys. Rev. B 78, 161401 (2008)], by taking rigorously into account the pump irradiance and emitters lifetime modifications in the system. We finally apply this formalism to describe gain–assisted propagation in a dielectric–loaded surface plasmon polariton waveguide.
Nonresonant dielectric hole burning spectroscopy of supercooled liquids
1997
The nonexponential response of propylene carbonate and glycerol near their glass transitions could be selectively altered using nonresonant spectral hole burning (NSHB) experiments. This observation provides evidence of the existence of a distribution of relaxation times in these supercooled liquids. NSHB is based on a pump, wait, and probe scheme and uses low-frequency large amplitude electrical fields to modify the dielectric relaxation. The temporal evolution of the polarization of the sample is then measured subsequent to a small voltage step. By variation of a recovery time inserted between pump and probe, the refilling of the spectral features could be monitored and was found to take …
A modified ansatz for explicitly correlated coupled-cluster wave functions that is suitable for response theory
2009
A modified ansatz for explicitly correlated coupled-cluster wave functions with a single correlation factor is set forward. It is based on the fixed amplitude ansatz of Ten-no [Chem. Phys. Lett. 398, 56 (2004)] to which an extra term is added that allows for the explicitly correlated description of singly excited configurations. The new approach has been implemented for coupled-cluster singles and doubles with the aid of automated techniques. Numerical results are presented for vertical excitation energies, and ground and excited state equilibrium distances and harmonic frequencies of diatomics. The new approach is shown to provide a nearly unbiased description of ground and predominantly s…