Maria-Novella Piancastelli, Sorbonne Université, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement, Paris, France; Department of Physics and Astronomy, Uppsala University, Sweden.“Femtosecond structural dynamics
Sorbonne Université, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement, Paris, France; Department of Physics and Astronomy, Uppsala University, Sweden.
“Femtosecond structural dynamics of core-excited and core-ionized water molecules”
Chair: Dr Nadja Doslic (Rudjer Boskovic Institute, HR)
Abstract: Results on femtosecond dynamics of a core-excited and core-ionized prototypical system, the water molecule, will be presented.
Such dynamics can be investigated by using an “internal clock” or a time-resolved source.
In particular, one of the methods, the so-called core-hole-clock, uses the decay time of a core excitation as a reference clock for other processes in the system studied. Typically, the decay of a core excitation yields a spectral signature that is characteristic for a given system. If other processes are taking place during the core-hole decay, they will also have their own identifiable spectral signature. The core-hole lifetime can then be used as ‘internal clock’ to study some dynamical phenomena. The most widely studied one is the so-called ultrafast fragmentation, meaning molecular fragmentation taking place on the same timescale of the core-hole decay. If nuclear motion in a photoexcited molecule leads to the breaking of a chemical bond before electronic relaxation, the decay takes place in the fragment rather than in the intact molecule. The spectrum of the fragment will then be superimposed to the one of the intact molecule, and will be possible to assign. Ultrafast fragmentation of core-excited water will be discussed, by resonant Auger spectroscopy and electron-ion coincidence studies at synchrotron sources.
The other method implies the use of a time-resolved light source, such as a HHG or a free-electron laser. In this framework, recent results obtained at the EuXFEL will be presented. The ultrafast structural dynamics of water following inner-shell ionization are a crucial issue in high-energy radiation chemistry in liquid media. We have exposed isolated water molecules to a short x-ray pulsefrom a free-electron laser, and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we can image dissociation dynamics of individual molecules in unprecedented detail. We reveal significant molecular structural dynamics in H2O2+, such as asymmetric deformation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. We thus record a molecular movie of a water molecule, which reveals dynamical patterns relevant as initiating steps of subsequent radiation damage processes in a liquid environment.
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(Wednesday) 15:00 - 16:00
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