Date : 2012. 11. 19, 2:00 PM Place : Mogam Hall, Bldg.500 - Abstract- Femtosecond time-resolved spectroscopy can observe photochemical processes in real time and map out the pathway from a reaction educt to a product. We combine gas-phase spectroscopy and high-level theory to resolve the mechanism of excited state processes in isolated molecules, predominantly building blocks of DNA. In real biological systems, biomolecules are embedded in a structured environment and interactions with the local environment affect molecular properties. Whether gas-phase experiments offer relevant contributions towards the understanding of biologically relevant processes is therefore heavily disputed. We bridge the gap with experiments on molecular clusters that reproduce crucial structural elements, such as base-pairing and base-stacking in DNA. The information content of femtosecond experiments is limited by the Heisenberg uncertainty principle (△E×△t > h/(4pi)) and is rarely sufficient for the spectroscopic assignment of molecular structure. Experiments on impure samples or samples containing unknown molecular structures are therefore difficult. With a novel technique of correlated rotational alignment spectroscopy (CRASY), we correlate high-resolution rotational structure with femtosecond pump-probe data. This technique allows the isomer-selective investigation of electronic structure and dynamics, the simultaneous characterization of all species in an impure sample, and the assignment of fragmentation channels of molecules and clusters.