Probing electronic processes in large molecules with attosecond time resolution

by Prof. Francesca Calegari (CFEL-DESY, Hamburg Universität)

Tuesday 16 Oct 2018, 13:00 → 14:00 Europe/Berlin

E1.173 (European XFEL, main building, campus Schenefeld)

Attosecond science is nowadays a well-established research field, which offers formidable tools for the investigation and control of electronic processes [1,2]. The possibility to study molecules of increasing complexity with attosecond time resolution paves the way to disclosing the role of the electron dynamics in the photo-chemistry and photo-biology of complex systems. In this context, we have recently demonstrated that attosecond pulses can initiate charge migration between different functional groups of aromatic amino-acids [3]. In this talk I will first present a time-resolved study of photo-fragmentation of the nucleobase adenine, one of the key building blocks of DNA. Our most intriguing observation is that a stable dication of the parent molecule can be produced if (and only if) the probing NIR pulse is very briefly delayed from the XUV pulse. Our experimental and theoretical findings indicate that this short delay corresponds to the lifetime of the inner valence hole. The process also evidences the presence of a laser-assisted stabilization of the nucleobase. In the second part of the talk I will show the results we have recently obtained for a very large polyatomic molecule, namely the C60 molecule. Here we have investigated delays in photoemission after exciting the Giant surface Plasmonic Resonance (GPR) around 20 eV. Clear signatures of the collective electron dynamics initiated by the XUV pulse can be extracted from the experimental data. [1] F. Krausz and M. Ivanov, “Attosecond physics,” Rev. Mod. Phys. 81, 163 (2009) [2] M. Nisoli et al, Chem Rev 117 10760 (2017) [3] F. Calegari et al, Science 346, 336 (2014)