Le LISA, Laboratoire Interuniversitaire des Systèmes Atmosphériques est une unité de recherche de structure originale dépendant des Universités Paris Est Créteil et Paris Diderot, et du CNRS (UMR CNRS 7583).
Le LISA compte environ 130 personnes, dont 50 enseignants-chercheurs et chercheurs (CNRS & IRD), 36 ITA-IATOS et environ 45 post-doctorants, doctorants et étudiants de Master.
Il dispose d'un important potentiel technique et expérimental réparti sur 3.600m2 de locaux à Créteil et d'une antenne opérationnelle sur le site Paris Rive Gauche, incluant aussi des équipements lourds. Les recherches y sont développées autour d’un thème générale : l’Atmosphère (comme le nom du laboratoire l’indique), Ses principaux thèmes de recherche portent ainsi sur la compréhension du fonctionnement des atmosphères terrestres et planétaires, et des impacts liés à la modification de la composition de l'atmosphère par les activités humaines. Les méthodes utilisées sont fondées sur des observations en atmosphère réelle, sur de la simulation expérimentale en laboratoire et de la modélisation numérique.
Pour mener à bien ces recherches, le LISA regroupe des scientifiques de plusieurs disciplines : physiciens, géochimistes, environnementalistes et une majorité de chimistes. Ce dernier aspect est une de ses caractéristiques importantes par rapport aux autres laboratoires du domaine. Un département technique (doté de 4 pôles : chimie, instrumentation, terrain et informatique) et un département administratif sont en soutien des activités de recherche.
Date: 14 6 月 2017 - 14:40
Desc: A better understanding of the complex organic chemistry occurring in the methane rich atmosphere of Titan can be achieved via the comparison of observations with results obtained by theoretical models. Available observations are still few but their analysis requires the knowledge of a large set of data, namely frequencies and absolute band intensities. Cross sections are also needed to develop the chemical schemes of photochemical models, in particular the schemes leading to the formation of haze particles visible on Titan. Unfortunately, some of these parameters are not well known. especially if one takes into account the extreme physical conditions of the studied object. This lack of data is particularly enhanced for polyynes because these compounds are highly unstable at the usual pressure and temperature conditions of a laboratory and therefore are very difficult to study. We have developed UV and IR studies, coupling experimental and theoretical approaches, in order to extrapolate the parameters available for short polyynes to longer carbon chains. In the mid-UV range, when the length of the chain increases, the absorption system of polyynes is shifted to longer wavelength and its oscillator strength increases linearly. In the IR range, with the increase of the number of carbon bonds, the positions of the CCC and CCH bending modes shift to lower energy, the latest converging rapidly to a fixed value of 620.5 cm−1 for an infinite length polyyne. Implications for detection and evolution of polyynes in Titan's atmosphere are emphasised.
Date: 13 Mar 2015 - 16:02
Desc: The polyol process is one of the few methods allowing the preparation of metal nanoparticles in solution. Hexagonal close packed monocrystalline Co nanorods are easily obtained in basic 1,2-butanediol at 448 K after a few minutes using a Co(II) dicarboxylate precursor. By using a combined experimental and theoretical approach, this study aims at a better understanding of the growth of anisotropic cobalt ferromagnetic nanoparticles by the polyol process. The growth of Co nanorods along the c axis of the hexagonal system was clearly evidenced by transmission electron microscopy, while the mean diameter was found to be almost constant at about 15 nm. Powder X-ray diffraction data showed that metallic cobalt was generated at the expense of a non-reduced solid lamellar intermediate phase which can be considered as a carboxylate ligand reservoir. Density functional theory calculations combined with a thermodynamic approach unambiguously showed that the main parameter governing the shape of the objects is the chemical potential of the carboxylate ligand: the crystal habit was deeply modified from rods to platelets when increasing the concentration of the ligand, i.e. its chemical potential. The approach presented in this study could be extended to a large number of particle types and growth conditions, where ligands play a key role in determining the particle shape. Graphical abstract: Control of the anisotropic shape of cobalt nanorods in the liquid phase: from experiment to theory… and back
Date: 14 6 月 2017 - 14:39
Desc: Geometrical parameters and harmonic vibration frequencies of polyynes HC2nH (n = 1−8), cyanopolyynes HC2n-1N (n = 1−7), and dicyanopolyynes NC2nN (n = 1−8) have been calculated with various density functionals using the Dunning triple-ζ basis set. For selected data, we propose extrapolation formulas for longer molecules of the series. Bond lengths and electron localization function analysis indicate that a marked bond alternation persists in molecules as long as HC30H. The evolution along the series of some vibration frequencies and their accuracy for the identification of long molecules in extraterrestrial systems are also discussed.
Date: 28 1 月 2020 - 11:45
Desc: Absorption wavelengths and oscillators strengths have been calculated for the allowed low-energy electronic transition $^1\Sigma^+ \leftarrow ^1\Sigma^+$ of monocyanopolyynes (HC$_y$N, $y = 1-13$), $^1\Sigma_u^+ \leftarrow ^1\Sigma_g^+$ of polyynes and dicyanopolyynes (HC$_y$H and NC$_y$N, $y = 1-40$). For $y > 18$, the geometries were extrapolated from DFT optimization of the shortest members. Extrapolation formulas have been drawn up for longer chains, the asymptotic values of those yield an estimation of the absorption wavelength (ca. 400 nm) of the hypothetical carbon allotrope carbyne.
Date: 27 9 月 2013 - 17:23
Desc: no abstract
Direction du LISA
Maison des Sciences de l’Environnement 4ème étage
UPEC Campus Centre
61, avenue du Général de Gaulle
94010 CRETEIL CEDEX
contact@lisa.u-pec.fr / 01.45.17.15.60