Prof. Graham A. Worth (University College London, UK)
Mercredi 29 janvier 2020 à 10h30 (salle Magat)
"Quantum Molecular Dynamics : Simulating Fundamental Chemistry at the Femtosecond Timescale"
Résumé
Time-resolved spectroscopy using techniques such as pump-probe pulsed
lasers can reveal details of reactivity and chemical reactions as they
occur. To help understand what is seen, and provide a molecular picture
for the signal obtained, computer simulations are indispensable [1]. At
these short time-scales, the quantum nature of matter cannot be ignored
and we need to solve the time-dependent Schroedinger equation. Over the
last couple of decades, we have been developing a powerful computer code
[1] to accurately solve this equation for a range of systems. Of
particular interest to me are photo-activated processes. Here, knowing
the competition between different pathways is key to understanding the
behaviour of molecules and the properties of materials. What are termed
non-adiabatic transitions [2], where a system is able to to change
electronic state instantaneously in a non-radiative process, have been
shown to play a special role. They are important in a range of
photo-chemical and photo-physical systems, including the photochemistry
of many organic molecules and even providing the photo-stability of DNA
bases and the photoswitching of chromophores inside proteins. In this
talk I will describe the aims and basic ideas of the fundamental
research into nuclear motion, with examples that demonstrate
our present capabilities and knowledge in how molecules behave after
absorbing a photon.
[1] Fielding, H. H. and Worth, G. A., Chem. Soc. Rev. (18) 47 : 309-321
[2] Worth, G. A., Comp. Phys. Comm. (20) 248 : 107040
