Adsorption on interstellar analog surfaces : from atoms to organic molecules

Abstract : Gas-grain interaction plays an important role in the chemistry of the cold interstellar medium and protoplanetary disks. A key parameter for modeling the exchange between grain surfaces and gas phase is adsorption energy, Ea. This work aims to develop a reliable and systematic experimental/theoretical approach to determine the adsorption energies of relevant atoms and molecules on models of interstellar grain surfaces. Employed experimental technique is the Temperature Programmed Desorption. Developed experimental protocol and data treatment technique based on distribution of adsorption energies and use of a set of heating rates enable to determine the coupled parameters of Polanyi-Wigner equation: adsorption energy Ea and prefactor N. Computational chemistry approach, Density Functional Theory (DFT) as implemented in Vienna Ab initio Simulation Package (VASP) is used to get the insight on the behaviour of the surface-adsorbate systems at the atomic level. This approach allows as well to determine adsorption energies. A presence of multiple adsorption sites with different adsorption energies is predicted. Methanol CH3OH adsorption on graphite is used as a known example to validate the technique. Ar/Kr/Xe adsorption on water ice is studied as a case relevant for planetology. Acetonitrile (CH_3CN) and methyl isocyanide (CH_3NC) adsorption on water ice, quartz and graphite is investigated since those two molecules are both detected in the interstellar medium. Adsorption energies determined in this work will be included in KIDA database.
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Mikhail Doronin. Adsorption on interstellar analog surfaces : from atoms to organic molecules. Chemical Physics [physics.chem-ph]. Université Pierre et Marie Curie - Paris VI, 2015. English. ⟨NNT : 2015PA066254⟩. ⟨tel-01238850⟩



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