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Etude par modélisation moléculaire de la séparation isotopique du lithium par des éther-couronnes dans l'éthanol

Abstract : The isotopic separation of lithium ion isotopes is studied at the CEA in Pierrelatte using a liquid chromatography technique. Exchange systems are composed by crown-ethers grafted on silica (12C4, 15C5, B15C5, DB15C5, 18C6, B18C6). Lithium is introduced as a salt melted in ethanol. This work concerns the theoretical study of lithium isotopic exchange reactions with those systems. After a brief presentation of isotope separation techniques and isotopic effects (Chap.I), we describe the methods of theoretical chemistry used in this work (Chap. II). In chapter III, we test AM1 and PM3 semi-empirical methods for the treatment of Li+ /crown-ether species. Then, we calculate isotopic separation factors via ab initio and semi-empirical calculations for the exchange reactions in vacuum. The different crown-ethers are considered with and without graftings arms. Studies of exchange reactions in ethanol are presented in chapter IV. First, each species of the reaction are solvated by a few ethanol molecules. Isotopic separation factors calculated show a large effect of the solvent on the exchange reaction. The effect of the grafting arm has been investigated using hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics for species with the 12C4. Trajectories have been generated successively with 7Li and 6Li. Atomic velocity autocorrelation functions have allowed the access to vibrational frequencies necessary to calculate isotopic separation factors. The last chapter is devoted to methodological developments made during this Ph.D . We propose an approach to treat long range electrostatic interactions in hybrid QM/MM method, relying on a lattice summation technique.
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Submitted on : Thursday, March 29, 2018 - 10:39:36 AM
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François Dehez. Etude par modélisation moléculaire de la séparation isotopique du lithium par des éther-couronnes dans l'éthanol. Autre. Université Henri Poincaré - Nancy 1, 2002. Français. ⟨NNT : 2002NAN10026⟩. ⟨tel-01746524⟩



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