Seminars Archive

XUV induced ultrafast dynamics in large polyatomic systems.

Abstract
Electron correlation in a molecule is one of the main difficulties of the N-bodies problem. One mean to enhance multielectronic effects is to use extreme ultraviolet light (XUV) in order to ionize inner-valence electrons of complex polyatomic systems. Thus, the produced cationic states result from a higher order photo-excitation processes (such as “2-holes, 1particle”) and their dynamics lead to considerations out of the frame of the Born-Oppenheimer approximation. Recent developments in ultrafast science concerning the XUV ultrashort pulses sources, produced by high harmonic generation (HHG), allow studying these mechanisms from the hundreds of femtoseconds (1 fs = 10−15 s) timescale up to the attosecond (1 as = 10−18 s) timescale [1]. Here, I will present studies of these processes performed on carbonaceous and biological molecules thanks to a XUV-pump IR-probe spectroscopy scheme coupled to a velocity map imaging spectrometer (VMIS) [2]. More specifically, we have studied, in Polycyclic Aromatic Hydrocarbons (PAHs), the evolution of highly excited cationic states [3] and the effect of the molecular potential during the photoionization process. In addition, we have examined the role of the ultrafast charge dynamics induced by XUV photo-ionization on fragmentation mechanisms in the caffeine biomolecule. The observed processes are entire part of a multi-scale approach of the ultrafast molecular physics and allow a better understanding of the implication of multielectronic effects and non-adiabatic couplings in complex polyatomic systems.
[1] F. Lépine et al., “Attosecond molecular dynamics : fact or fiction ?”. Nature Photonics, 8:195, 2014. [2] V. Loriot et al., “Resolving XUV induced femtosecond and attosecond dynamics in polyatomic molecules with a compact attosecond beamline,” J. of Phys. Conf. Series, 635:012006, 2015. [3] A. Marciniak et al., “XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment,” Nat. Commun., 6:7909, 2015.