My group is currently working in two different areas: The spectroscopy of mass-selected ions in vacuo and the characterization of supramolecular assemblies and nanocrystals at very high pressures.
In the first area, we combine mass spectrometry with laser spectroscopy to characterize positively and negatively charged ions in a very well-defined chemical environment. Much of the behavior of important molecular species is only known in a condensed phase environment (mostly solutions), where interaction with the solvent changes some of the properties of the solute. In order to unravel the effects of solvent-solute interactions, we want to understand the intrinsic properties of the solute and study them as isolated entities in vacuo. There are two main areas of interest at present:
(A) Reductive activation of CO2 by transition metal catalysts:
The development of efficient routes towards generation of sustainable fuel sources by electrochemical reduction of CO2 is an important goal for catalysis research. So far, solvent effects in catalysis are largely not understood or even characterized. Mass-selected clusters of metal anions with CO2 serve as a model system for the reductive activation of CO2 by a catalyst under complete control of the composition and size of the solvation environment. Vibrational spectroscopy and electronic structure calculations are used to obtain molecular-level information on the interaction of solvent with the catalyst-CO2 complex and their effects on one-electron reduction of CO2. If you would like to read more about this, click here.
(B) Photochemistry and electronic structure of transition metal complexes:
We gain a deeper insight into the electronic and geometric structures, and the inter- and intramolecular forces in transition metal complex ions. The experiments contribute valuable information, e.g., on the electron donation/back-donation in metal- and metaloxide-ligand complexes and electron-binding energies. Another example in this program area is the investigation of the photochemistry of species that are relevant to metal-organic reactions, e.g., the photochemistry of chromate esters, which are important intermediates in the oxidation of alcohols by chromate. If you are interested in this area, you can read more here and here.
Energy flow in molecules
All chemical reactions are governed by the nuclear dynamics of molecules, in other words, their patterns of vibrational motion. Therefore, the way in which vibrational energy flows through, and is redistributed in, molecules after excitation has significant impact on the understanding of chemical reaction dynamics, and for the prospect of coherent control of chemical reactions.
Moreover, characterizing energy flow through nanoscale systems has become a critical issue as technology utilizing the progressively smaller sizes of electronic devices encounters the destruction limit of energy density. We follow a new experimental approach to study the flow of energy as it drains out of a certain vibrational mode and arrives at a well-defined place in a molecule. In this approach, we use model systems where the binding energy of an electron in a negatively charged molecule is less than the energies for certain vibrational transitions. This way, we can follow the flow of energy in a molecule by monitoring electron loss and analyzing the kinetic energy distribution of these electrons with high-resolution photoelectron spectroscopy. If you would like to know more about this topic, you can click here.
Supramolecular chemistry and materials at very high pressures
Nanostructured materials (quantum dots, nanowires, nanocrystals) have led to a large research field in the last few years. While there is a huge body of work on their synthesis, the molecular-level details of their interaction with their chemical environment is largely not explored, as is the size dependence of many of their structural properties. High pressure experiments offer a way to tackle such questions.
At relatively low pressures (a few hundred MPa), only intermolecular distances are varied by the application of pressure. This is much less perturbative than variation of temperature or chemical composition. The behavior of nanocrystals at these low pressures yields information on the properties of the interface between the nanocrystals and their chemical environment, including their protective ligands.
Higher pressures (GPa range) can result in phase changes in the solvent or in the nanocrystals themselves. The former will again lead to a change in the interaction of the nanocrystal with its environment. The latter afford access to new materials with new optical and electronic properties. We use photoluminescence spectroscopy and Raman microspectroscopy to study these phenomena.