Le dispositif PIRENEA dans l'étude des interactions gaz/grain dans la chimie interstellaire: mise en place d'une procédure expérimentale.

摘要

Gas-grain interactions play an important role in interstellar chemistry, both in UV-irradiated regions and in the more embedded regions of molecular clouds where icy mantles are formed on dust grain surfaces. However, astrophysical models suffer from the lack of experimental data in particular those involving on the interaction of gas with isolated grains.The present PhD thesis aims at experimentally studying gas-grain interactions on nanograins like polycyclic aromatic hydrocarbons (PAH) at several temperatures. The PIRENEA ("Piège à Ions pour la Recherche et l'Étude de Nouvelles Espèces Astrochimiques") laboratory set-up was developped according to these specifications: it combines the trapping capabilities of the Fourier Transform Mass Spectrometry analysis of an Ion Cyclotron Resonance cell (FTICR-MS) with cryogenic shielding to produce and isolate PAH ions in interstellar conditions. It is also equipped with several photon sources and a gas inlet interface that enable to probe gas-grain interaction properties.Our study focuses on the reactivity of C24H11+ (deshydrogenated coronene cation) with H2O molecules at low temperatures between 35 and 300 K. First, we will show how the neutral gas density in an ICR cell can be quantified at different temperatures both by traditional pressure measurements and by measuring the collisional damping of the ion cyclotron motion. These results allow us to measure the rate constant for the "C24H11+ + H2O" reaction as a function of the trap temperature. No temperature dependence has been observed. The results are confronted to ab-initio calculations.