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 Karl Franzens University Graz

Graz University of Technology 

Ultrafast processes in molecules investigated by femtosecond time-resolved spectroscopy
Dr. Markus Koch
Institute of Experimental Physics, Graz University of Technology
17:15 - 18:15 Tuesday 07 March 2017 TUG P2

Within the last two decades ultrafast laser spectroscopy has led to fundamentally new insights of dynamical processes in atoms, molecules, clusters and condensed matter. In this talk I will introduce femtosecond time-resolved spectroscopic methods with a focus on the investigation of non-adiabatic processes in isolated molecules. Ultrafast dynamics are studied by pump-probe schemes, which will be explained including the generation and characterization of femtosecond laser pulses.
Current developments in the field include the application of increasingly higher photon energies obtained from high-order harmonic generation. I will present transient photoionization experiments with vacuum ultraviolet pulses on gas-phase perylene molecules. [1] Comparison to the widely used method of multiphoton probing clearly demonstrates the influence of the applied probing scheme and the related risk of misinterpreting the observed transient signals. [2]
As a second example of current developments, I will introduce the method of photoelectron-photoion coincidence detection in time-resolved photoionization. The high differentiability of coincidence detection allows to observe and disentangle competing relaxation channels in a molecule and to follow the fragmentation behavior and time evolution of each channel separately. The method is demonstrated by investigating the non-adiabatic relaxation dynamics in acetone molecules triggered by photoexcitation of high-lying Rydberg states. [3,4]
I will close with an outlook on femtosecond experiments in superfluid helium nanodroplets, aiming at time-resolved dynamical studies in a controlled microsolvation environment at very low temperatures.

References
[1] M. Koch, T. J. A. Wolf, J. Grilj, E. Sistrunk, M. Gühr, J Electron Spectrosc Relat Phenom 197, 22–29 (2014).
[2] M. Koch, T. J. A. Wolf, M. Gühr, Phys Rev A 91, 031403 (2015).
[3] P. Maierhofer, M. Bainschab, B. Thaler, P. Heim, W.E. Ernst, M. Koch, J. Phys. Chem. A 120, 6418-6423 (2016)
[4] M. Koch, P. Heim, B. Thaler, M. Kitzler, W.E. Ernst, under review (2017)