Thèses

Jeudi 8 Juillet 2021 à 14h00.

Photodissociation and relaxation dynamics of small Polycyclic Aromatic Hydrocarbon (PAH) monomer and dimer cations stored in electrostatic ion storage rings

''Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous complex molecules present in different regions of the universe. They are expected to be possible carriers of the unidentified infrared bands and emitters of the diffuse interstellar bands. The energy relaxation dynamics of such isolated species are of particular interest in understanding their lifetime, stability, and role in the universe. Electrostatic storage devices, such as Mini-Ring and DESIREE used in the present work have proven to be powerful tools to investigate such isolated molecules over long time observation up to seconds in ultrahigh vacuum. Ion beams of cationic PAHs monomer and dimer were produced using electron cyclotron resonance ion sources under special tuning conditions and stored in the two storage rings. The present results about phenanthrene cation confirmed the existence of a fast radiative cooling attributed to recurrent fluorescence. Conversely, for PAH dimer cations, the radiative cooling process is much slower than for monomer cations because of the absence of the recurrent fluorescence process. The photo-dissociation spectra of dimer cations show two peaks attributed to the charge resonance (CR) and the local excitation bands. These spectra are interpreted using a semi-empirical model and DFTB-EXCI theory. Naphthalene dimer cations were stored up to 30 s in the cryogenic ring DESIREE. The evolution of the CR line was measured as a function of storage time. The time evolution of the center of the CR line is used to estimate the cooling rate of the naphthalene dimer cation.

Directeur de thèse / thesis director:
BERNARD Jérôme
Membres du jury / members of the jury:
Mme. DOMARACKA Alicja
M. MANIL Bruno
M. COTTANCIN Emmanuel
Mme. JOBLIN Christine
M. BERNARD Jérôme
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