Thèse

Jeudi 24 Septembre 2026 à 14h00.

Dynamics in Complex Molecules: From Femtosecond Nuclear Motion to Attosecond Electron Scattering

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Directeur de thèse / thesis director :
Franck LEPINE, Saikat NANDI

Membres du jury / jury members :
Thomas NIEHAUS, Professor, Université Claude Bernard Lyon 1
Caterina VOZZI (Rapporteur), Research Director, IFN, Italian National Research Council (CNR)
Oksana TRAVNIKOVA (Rapporteur), Chargée de recherche, CNRS, Sorbonne Université
Samuel COHEN (Examinateur), Professor, University of Ioannina
Saikat NANDI
Franck LEPINE

Résumé / Abstract :

When an atom or a molecule absorbs a photon, it undergoes transformations that initiates a wide range of physical, chemical and biological processes. Ionization, defined as the removal of an electron following the absorption of a photon, plays a central role in phenomena like chemical evolution of the interstellar medium, radiation induced damage in biological matter and many other photochemical and photophysical mechanisms. Despite its importance, the first stages of ionization are still difficult to investigate experimentally. Electron dynamics, including the emission of electron takes place on attosecond timescales, while the subsequent redistribution of charge and nuclear motion occur over femtosecond timescales that are not easily accessible with conventional spectroscopic techniques. However, these initial steps determine the evolution of the system, thereby accessing these ultrafast dynamics is therefore essential for a detailed understanding of light-matter interaction.

Recent advances in light sources that can reach sub-femtosecond regime, have enabled the access to these timescales. High order harmonic generation, as a tabletop source, provides, coherent ultrashort pulses in the extreme ultraviolet (XUV) range, enable the observation of electron dynamics with attosecond resolution. In this work, several experimental methods are presented that have been used to explore the ionization driven dynamics in molecular systems in the gas phase. Photoionization time delays are measured using the RABBITT (Reconstruction of Attosecond Beating by Interference of Two-photon Transitions) photoelectron interferometry in two DNA bases, and sulphur hexafluoride (SF6), revealing the influence of molecular structure, charge distributions and resonances on electron quantum scattering.

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