Lund University

MAX IV laboratory




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Research projects in atomic, molecular and cluster physics

Imaging of small molecules

N2 image

Atoms and molecules in electronically excited states decay via various processes which lead to bond breaking and ion formation, producing neutral and charged constituents that react with their neighbors. These processes occur everywhere, from car engines to industrial chemical plants. Ionization processes occur naturally in the Earth's upper atmosphere and at the Earth's surface and are largely responsible for radiation damage in biological molecules. Generally high-energy photoionization or collisional ionizatioin leads to a greater the number of possible reaction pathways for higher energy transfer resulting in greater “damage” to the system.

On a fundamental level we are able to image the molecule by careful measurement of the ion trajectories. This provides a tool for connecting molecular geometry in fragmentation to kinematics and to the time scale of competing processes. This is a major field of research and momentum spectroscopy can help to answer fundamental questions which play an important role in many branches of physics, chemistry and biology.

Responsible Scientist: Stacey Sorensen

Cluster photoionization

Cluster

Photoinduced processes in complex systems can be modeled as a sequence of events initiated by the absorption of a photon. Photoionization of an atomic electron is followed by electronic relaxation which results in a migration of charge within the atom. The need to understand how this initial event leads to higher ionization states and dynamic effects in complex systems such as biomolecules or nanostructured materials is motivated by biological processes and by possible light-harvesting applications. The extreme complexity in understanding the series of sequential events lies in the interplay between electrons and ions especially when the times scales are similar. This phenomenon, called the break down of the “Born-Oppenheimer” approximation, is surprisingly common for large molecules and its investigation is one of the great challenges of this century. Nature takes advantage of such situations to control the flow of energy to activate a structural or a chemical change for instance to tune molecular properties to the local environment.

Weakly bound, atomic and molecular, clusters have been the subject of many studies to investigate structures, dynamics and energetics of nano-scale objects, with the goal to understand the evolution of their properties from isolated atoms to the bulk solid. The ability to tailor them in large variety of ways, for example size, geometry, chemical environment..., make these clusters ideal as model systems to understand how the primary sequence of processes is affected by surrounding atoms or molecules.

Responsible Scientists: Mathieu Gisselbrecht, Noelle Walsh

Femto- and attosecond science

C2H2 pump-probe

Femtosecond spectroscopy is a fantastic tool to probe ultrafast processes/dynamics in molecules and clusters, such as proton transfer in ammonia clusters, or charge transfer in photo-excited metallic complexes.

Attosecond pulses created by high harmonic generation (HHG) in gases allow us to study fundamental light-matter interaction processes with novel experimental techniques. The ultrashort light pulse leads to the creation of a wave packet that can be exploited to investigate attosecond dynamics in ionized systems. We apply interferometric techniques to access the correlated multi-electron dynamics in complex systems aiming to monitor in real time charge migration/transfer.

Responsible Scientist: Mathieu Gisselbrecht

Calculation of electronic structure in molecules

Water potentials

Experimental data can often illuminate dynamics, but for polyatomic molecules the complexity of spectra prohibits insight based primarily on spectroscopic data. Modern quantum chemistry techniques offer the possibility to calculate the potential surfaces involved in molecular excitation/deexcitation processes both in the neutral, cation and dication species. Knowledge of these potential surfaces are also essential for connecting fragmentation channels to electronic states and to specific electronic decay channels. This research is carried out in close collaboration with the Theoretical Chemistry group at Lund University using computer resources at LUNARC (Centre for Scientific and Technical Computing at Lund University). The MOLCAS software which is used in the research project to model the small molecules under investigation has been developed by the theoretical chemistry group in Lund.

Calculations of the potential surfaces in the core-excited states as well as the dication potential surfaces are central to explaining the selectivity or kinematics of dissociation processes.

Responsible Scientist: Anna Sankari

Instrument development: imaging spectroscopies

Instrumentation for carrying out multicoincidence expeirments between ionized fragments and photoelectrons is developed within the group. Design and characterization studies have been carried out for a high-resolution three-dimensional ion imaging system for use with synchrotron radiation, and a full three-dimensional imaging system has been designed and constructed for pulsed XUV laser systems.

Responsible Scientist: Mathieu Gisselbrecht

3D momentum imaging