Mission Statement

The aim of the project encompasses real-time determination of ultrafast structural dynamics of molecular and biomolecular systems.

The first main target is the determination of the structures while they explore the energy landscapes. These energy landscapes are not static but fluctuating due to the dynamical interactions of these structures with the surroundings (such as liquid solvent shells, or the protein backbone). The ultrafast nature of these fluctuations necessitate femtosecond time resolution for the structure-resolving spectroscopic techniques. The second main target is the determination of biomolecular structures that undergo substantial geometric rearrangements induced by optically triggered chemical reactions (photochemistry). Chemical reactions studied include hydrogen and proton transfer, electron transfer, bond fission, ring-opening/closure and cis/trans isomerizations. These activities fall in the field of ultrafast chemistry, also known as femtochemistry.

Methodology

The powerful method that has been pursued since 1997 is ultrafast vibrational spectroscopy. Here the dynamics are studied by inspection of mid-infrared (IR) active or Raman-active vibrational marker modes. Structural dynamics in the electronic ground state have been investigated with IR pump/ IR probe and IR photon echo spectroscopy. Dynamical rearrangements of structures induced by an optical trigger pulse tuned to an electronic resonance (a UV/VIS-pump) have been followed with time-delayed transmission changes of mid-IR probe pulses or by collection of resonance Raman-emission.

Investigated Systems

Ultrafast vibrational spectroscopy is used to study the structural dynamics of hydrogen bonds (in hydrogen-bonded liquids such as water, or biomolecular hydrogen-bonded complexes consisting of e.g. carboxylic acids), of chemical reactions such as hydrogen and proton transfer (e.g. photoacid-base neutralization reactions, and bimolecular donor-acceptor electron transfer), bond cleavage (e.g. NO-heme protein bond fission), ring-opening/closure reactions in photochromic switches and cis/trans isomerizations (e.g. in photoactive yellow protein), and of vibrational energy flow (intramolecular vibrational redistribution, vibrational cooling). In all these studies the dynamics are investigated of small model systems representing biomolecular structural motifs, or even on large biomolecules themselves (proteins).

Grouping of Activities

The activities can be grouped into three research directions:

Direction 1	Coherent vibrational response in the condensed phase For more information see: Subproject 1: Coherent vibrational response of hydrogen bonds Subproject 5: Ab initio simulations of nonlinear response
Direction 2	Ultrafast chemical reaction dynamics For more information see: Subproject 2: Bimolecular hydrogen, proton, and electron transfer Subproject 4: Photo-induced isomerizations
Direction 3	Vibrational energy flow For more information see: Subproject 3: Vibrational kinetics after elementary photochemical reactions

Further Information

The Team	Full list of current group members and list of alumni Members of Project 2-04
Recent Highlights	Quick link to recent highlights Breaking news in project 2-04 Complete list of highlights: Ultrafast molecular structural dynamics in the condensed phase
Publication List	Full list of scientific publications within this project Publication list of project 2-04 Important overviews Ultrafast vibrational dynamics of hydrogen bonds in the condensed phase. E. T. J. Nibbering and T. Elsaesser, Chem. Rev. 104 (4), 1887-1914 (2004). Ultrafast chemistry: using time-resolved vibrational spectroscopy for interrogation of structural dynamics. E. T. J. Nibbering, H. Fidder and E. Pines, Annu. Rev. Phys. Chem. 56, 337-367 (2005).