Search results for " pol"
showing 10 items of 21911 documents
Laser-induced enhancement of tunneling in NHD2
2012
We apply and explore techniques aiming at enhancing the tunneling by laser fields, originally developed for a one-dimensional model, to a complete six-dimensional vibrational model of the inversion motion in NHD(2). The computational study is performed with the multi-configuration time-dependent Hartree method. Assuming an ideal three-dimensional alignment we obtain a driven tunneling time twenty times smaller than the natural one, in rather good agreement with an oversimplified three-state model. In the case of one-dimensional alignment, a linearly polarized field leads to a poor enhancement of the tunneling probability, after averaging over the rotation about the alignment axis, whereas a…
A QM/MM Approach Using the AMOEBA Polarizable Embedding: From Ground State Energies to Electronic Excitations
2016
International audience; A fully polarizable implementation of the hybrid Quantum Mechanics/Molecular Mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent 1 relaxation of both the MM induced dipoles and the QM electronic density is used for ground state energies and extended to electronic excitations in the framework of Time-Dependent Density Functional Theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET30 scale is presented. Th…
Enhanced alignment and orientation of polar molecules by vibrational resonant adiabatic passage
2007
The authors show that polar molecules can be adiabatically aligned and oriented by laser pulses more efficiently when the laser frequencies are vibrationally resonant. The aligned molecules are found in a superposition of vibrational pendular states, each associated with the alignment of the rotor in one vibrational state. The authors construct the dressed potential associated with this mechanism. Values of detunings and field amplitudes are given to optimize the degree of alignment and orientation for the CO molecule.
pKa at Quartz/Electrolyte Interfaces.
2016
Acidity of silanol sites at the crystalline quartz/aqueous electrolyte (NaCl, NaI, KCl) interfaces are calculated from ab initio molecular dynamics simulations. pKa’s are found to follow a combination of the cationic and anionic Hofmeister series in the order pKa(neat solution) < pKa(NaCl) < pKa(NaI) < pKa(KCl), in agreement with experimental measurements. Rationalization of this ranking is achieved in terms of the microscopic local solvation of the protonated silanols and their conjugated bases, the silanolates SiO–. The change in the pKa is the result of both water destructuring by alkali halides, as well as of the specific cation/SiO– interaction, depending on the electrolyte. M…
Estimation des incertitudes de mesure sur bras polyarticulé portable par méthode de Monte Carlo
2013
International audience; Les bras polyarticulés portables ont progressivement évolué et sont de plus en plus utilisés dans l’industrie. Cependant, à l’heure actuelle, la traçabilité de ces dispositifs est difficile à effectuer et les incertitudes de mesures relatives à l’utilisation de ces appareils ne sont pas quantifiées. Le travail mené consiste à déterminer les incertitudes de mesures associées à la quantification, par un bras polyarticulé portable, des caractéristiques géométriques et dimensionnelles d’une pièce mécanique. Les travaux visant à élaborer un modèle d’incertitude de mesure, sont basés sur la méthode de Monte Carlo du supplément 1 du Guide pour l'expression de l'incertitude …
Phosphasalen group IV metal complexes: synthesis, characterization and ring opening polymerization of lactide.
2020
International audience; We report the synthesis of a series of Zr and Ti complexes bearing phosphasalen which differs from salen by the incorporation of two P atoms in the ligand backbone. The reaction of phosphasalen proligands (1a-1c)H2 with Zr(CH2Ph)4 led to different products depending on the nature of the N,N-linker in the ligand. In case of ethylene-linked phosphasalen, octahedral Zr complex 2a formed as a single stereoisomer in trans geometry. With the phenylene linker, it was shown by dynamic NMR spectroscopy that complex 2b exists as a mixture of trans and cis-β isomers in solution, both enantiomers (Δ and Λ) of the cis-β isomer being in fast equilibrium with respect to the NMR tim…
Cooperative N–H bond activation by amido-Ge(ii) cations
2020
N-heterocyclic carbene (NHC) and tertiary phosphine-stabilized germylium-ylidene cations, [R(L)Ge:]+, featuring tethered amido substituents at R have been synthesized via halide abstraction. Characterization in the solid state by X-ray crystallography shows these systems to be monomeric, featuring a two-coordinate C,N- or P,N-ligated germanium atom. The presence of the strongly Lewis acidic cationic germanium centre and proximal amide function allows for facile cleavage of N-H bonds in 1,2-fashion: the products resulting from reactions with carbazole feature a tethered secondary amine donor bound to a three-coordinate carbazolyl-GeII centre. In each case, addition of the components of the N…
Syntheses, Properties and Structures of [{(C 5 Me 5 ) 2 Nb} 2 NiTe 4 ] and [( t BuC 5 H 4 Nb) 2 Ni 5 Te 7 (Ph 2 PCH 2 PPh 2 ) 2 ]: The Quest for Tetr…
2007
The reaction of [Ni(COD) 2 ] with [Cp* 2 NbTe 2 H] (1; Cp * = η-C 5 Me 5 ) in the presence of Ph 2 PCH 2 PPh 2 (dppm) in boiling toluene gives black-violet [(Cp * 2 Nb) 2 NiTe 4 ] (3). If [Cp' 2 NbTe 2 H] (2; Cp' = tBuC 5 H 4 ) is used under similar conditions dark-brown [(Cp'Nb)2Ni5Te7(dppm)2] (4) is formed. The structures of 3 and 4 have been determined crystallographically. Complex 3 contains a severely distorted NiTe 4 tetrahedron to which two niobocene groups are coordinated. Density functional analysis of the electronic structure of the NiTe 4 building block shows that it is best described as an [Ni(η 2 -Te 2 ) 2 ] 2- fragment. The structure of 4 reveals the presence of two Ni 5 and T…
A Cationic Oligomer as an Organic Template for Direct Synthesis of Aluminosilicate ITH Zeolite
2020
There are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet-like crystal morphology, large surface area, fully four-coordinated Al species, and abundant acidic sites. Methanol-to-propylene (MTP) tests reveal that the Al-ITH zeo…
Two bimetallic layered materials with “Cu4Fe3” defective cubane units: syntheses, structures and magnetic properties of {[CuII(tn)]2[FeII(CN)6]}3·[Na…
2005
Abstract Reactions of the [Fe III (CN) 6 ] 3− anion with the [Cu II (tn)] 2+ ion (tn = 1,3-diaminopropane) afford the compounds {[Cu II (tn)] 2 [Fe II (CN) 6 ]}3·[Na 3 Fe III (CN) 6 ]·12H 2 O (1) and {[Cu n (tn)] 2 [Fe II (CN) 6 ]}·KCl·5H 2 O (2). Despite the differences concerning their asymmetric units, both structures present strong similar features: in both structures, the Cu(II) ion presents a square-base pyramidal CuN 5 environment and each [Fe II (CN) 6 ] 4− anion is linked to six Cu(II) ions through its six N atoms leading to infinite [Cu II (tn)] 2 [Fe II (CN) 6 ] layers which can be viewed as 2-D layered arrangement generated by the defective cubane units Cu 4 Fe 3 involving Fe-CN…