We aim at a better understanding of strongly-coupled electron and nuclear dynamics at conical intersection in neutral molecules. Conical intersections are ubiquitous in nature. They govern many elementary photophysical and photochemical processes, pertinent to a large number of research areas, from astrophysics, astrochemistry, and atmospheric chemistry, to biochemistry, biology and synthetic organic and inorganic chemistry. These elementary processes involve strongly-coupled electronic and nuclear degrees of freedoms, and dynamics that occurs on a timescale that can be as short as a few femtoseconds. XUV and X-ray pulses offer a promising route to study these ultrafast processes using, for instance, transient X-ray absorption spectroscopy or time-resolved photoelectron spectroscopy. Both techniques are currently being implemented.
Carlo Kleine, Federico Branchi, Maria Ekimova, Marc-Oliver Winghart, Suresh Yarlagadda, Jan Ludwig, Christian Strüber, Tobias Witting, Erik T. J. Nibbering, Arnaud Rouzée
We are developing time-resolved XUV and soft x-ray spectroscopy as a tool to investigate non adiabatic processes in isolated few-body systems and in extended molecules. Using the element- and site-specificity of core shell transitions from the 1s orbital to unoccupied molecular orbitals, we aim at visualizing ultrafast charge transfer processes in molecules. Dynamics at conical intersections, charge and energy transfer processes in push-pull chromophores and donor-acceptor molecules, and ligand-to-metal (et vice versa) charge transfer excited state dynamics in organometallic molecules are examples of the research directions. To this aim, we are developing sources of ultrashort XUV and soft x-ray pulse based on high-order harmonic generation. Additionally, experiments are performed at large scale facilities such as the FLASH free electron laser in Hamburg and the Linac Coherent Light Source (LCLS) at Stanford.
Evgenii Ikonnikov, Oleg Kornilov
These experiments aim at investigating ultrafast electronic dynamics in gas phase molecules using time-resolved photoelectron and photoion spectroscopy. Use of a one photon vis/VUV pump, one photon XUV probe configuration helps to fully explore the nature of photoinduced processes. Both pump and probe pulses can have tunable bandwidth and a fourier-limited duration. The experiments can ultimately reach sub-10fs resolution allowing to study coupling of electronic dynamics to fast molecular vibrations, such as C=C stretch vibrational bands in conjugated molecules. The pump pulses are obtained using the technique of supercontinuum generation with chirped-mirror compression. The probe pulses with photon energies up to 100 eV are selected from an HHG source by a time-compensatd monochromator. Studies of ultrafast internal conversion and isomerization with photoelectron amd photoion spectroscopy can be carried out to follow molecular dynamics down to the ground state with unprecedented resolution. Examples are studies of small conjugated molecules (indole, pentadiene, cyclobutadiene) and small molecules with strong coupling of the electronic and nuclear degrees of freedom (CH3I, NO2).