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Etudes théoriques à propos de l'origine exogène des molécules prébiotiques

Abstract : The hunt for prebiotic species in the interstellar medium is a major concern for understanding the possible role of interstellar chemistry in the synthesis of the molecules at the origin of life. This study was motivated by the fact that some amino acids are currently identified in meteorites but none are yet observed in the interstellar medium. On the one hand, we use DFT and ab-initio methods of quantum chemical calculations to study the relative stability of the isomers detected in the interstellar medium. This study leads to a "Minimum Energy Principle" (MEP) specifying that the most thermodynamically stable isomer corresponds to the larger abundance observed. Applying this principle, we evaluate the possibility of detecting new prebiotic species, particularly amino acids, in the interstellar medium. Then, within the same approach, we verify that the link between abundance and thermodynamic order is valid for amino acids in the meteorites, which allows us to constrain the formation conditions in the parent bodies. On the other hand, we use the plane-wave periodic method in order to study the sticking of molecular species on carbonaceous and icy interstellar grains. We show that there is an efficient selective adsorption for the different isomers. This could lead to an observational bias for the relative abundances of these isomers, which could provide a possible explanation for the few exceptions to the MEP.
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  • HAL Id : tel-00812072, version 1

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Marie Lattelais. Etudes théoriques à propos de l'origine exogène des molécules prébiotiques. Chimie théorique et/ou physique. Université Pierre et Marie Curie - Paris VI, 2008. Français. ⟨NNT : 2008PA066467⟩. ⟨tel-00812072⟩

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