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SPECTROSCOPIE ET STABILITE DES HYDROCARBURES AROMATIQUES POLYCYCLIQUES DANS LES CONDITIONS DU MILIEU INTERSTELLAIRE

Abstract : This work deals with the intramolecular dynamics of Polycyclic Aromatic Hydrocarbons submitted to interstellar medium conditions (isolated, rotationally cold but vibrationnally excited PAHs). Theoretical and experimental analyses of the two relaxation channels have been developed: IR emission or fragmentation. The IR absorption spectrum was obtained by classical Molecular Dynamics (on a Tight-Binding semi-empirical potential surface) coupled with the Adiabatic Switching semi-classical method in order to simulate any PAHs (even heavier than a hundred carbons). A new parametrization fitted to these aromatic systems and a quantum anharmonical DOS model were developed. This spectral simulation reproduces the main features as a function of the astrophysical relevant variables: role of the ionization (strong change in the spectrum profile and in the total absolute intensity), temperature influence (red shift, broadening and modification of the intensity of the peaks), anharmonicity (zero point energy, frequencies), structure effects (compactness, pentagonal cycle and size). The H-loss channel, induced by photon sequential absorption, of the fluorene cation (REMPI ionization) was studied using a supersonic molecular beams and a mass spectrometer. Our original method led to the determination of the absolute absorption cross-section, its attenuation with the number of absorbed photons and of the evolution of the decay rate in a relatively wide energetic range. A particular attention was focused on the data analysis techniques. A free fit of this rate is close to the PTD statistical model, but shows a strong discrepancy with the RRK model mainly at low energy. The activation energy obtained through these two models are compatible with that deduced from the Tight-Binding potential.
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https://tel.archives-ouvertes.fr/tel-00005244
Contributor : van Oanh Nguyen-Thi <>
Submitted on : Thursday, March 11, 2004 - 4:48:06 PM
Last modification on : Wednesday, October 14, 2020 - 3:56:43 AM
Long-term archiving on: : Wednesday, September 12, 2012 - 1:55:19 PM

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  • HAL Id : tel-00005244, version 1

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Van-Oanh Nguyen-Thi. SPECTROSCOPIE ET STABILITE DES HYDROCARBURES AROMATIQUES POLYCYCLIQUES DANS LES CONDITIONS DU MILIEU INTERSTELLAIRE. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2003. Français. ⟨tel-00005244⟩

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